Cliff.  Thanks for sharing your findings.  It does bring a potential problem to the forefront.  This is lengthy so try to stay with me on this.  I’ll try not to ramble.
 
Don’t take what I say as being okay with the distributor gears riding high.  It’s the lesser of two evils when the other side of the coin has the distributor gear too low on the shaft which does create some extreme wear issues.  To date, I’ve never seen a distributor gear or block wear issue with the distributor gear riding too high but have seen extreme wear problems when the distributor shaft is in a bind either from the gear being too low or the oil pump drive being too tight.  The problem is that the distributor gear placement measurement is not looked at by the majority of people that simply stab the distributor in the hole and take it for granted that all is well.  Whether by misinformation or by design, MSD has the Y distributor gears installed high on the shafts and they are simply not riding on the boss in the block.  If they had gone with the original Ford Y spec, there would be some instances where the shaft would be in a bind simply due to block manufacturing variances.
 
Now that I’m talking block variances, I do run across Ford blocks where the distributor holes are shallower than stock.  The factory obviously compensated for this with the original distributor installation and moved the gear upwards accordingly.  Unfortunately when the distributor is replaced with one where the gear is located according to the repair manual specification, the shaft is in a bind and the distributor gear and/or camshaft gear wears out prematurely.  In extreme cases, there is some galling going on at that lower distributor block boss.  I’ve also seen the block galling on the FE blocks but without having the distributor that was in the block when the galling too place, it’s difficult to determine the exact cause for the wear.
 
My first instance with distributor gear placement was with a rebuilt 351W back in the Seventies that was continually wearing out the distributor gears.  The original distributor was long gone and parts store distributors were being used.  Once it was figured out that the block distributor cavity was too shallow, it was a simple matter in raising the gear.  Since then, I’ve come across the same problem also with the 429/460 engines.  One of the fixes simply involved making an aluminum washer to go under the distributor flange to raise the distributor rather than relocate the distributor gear higher.  Pulling those gears off the shafts and relocating them can get dicey and especially where they’ve been off the shafts previously and already had new roll pin holes drilled in them.  You only get so many tries at this before the shaft is weakened from the additional roll pin holes.
 
So that brings me to a 292 block currently sitting in the shop.  The distributor hole on that block measures out at 4.975” rather than the desired 4.995-5.000”.  That creates a problem with using a distributor where the distributor gear is installed at the factory dimension.  Simply knowing the distributor hole depth in the block does allows me to insure that the distributor gear is at least not too low for that particular block. 
 
For a stock application, I do prefer that the gear does rest ‘freely’ on the block boss but the end play in the distributor does force an exactness to the distributor gear location and not a lot of leeway for the shaft being in a bind versus the gear riding high.  For an aftermarket distributor using bearings, then riding high for me is not a problem.  Thrust bushings in a distributor does create some unwanted loading within the distributor which is better concentrated at the block instead which at least does at least have a constant supply of oil.  Because the distributor shaft is end supported in the block, in my mind there’s no additional thrust load being imparted on the gear regardless of if the gear is at spec or riding slightly high.
 
I think the right answer to all this is for the gear to be resting on the blocks’ distributor pad while some distributor end play is still present.  It will be interesting to see what the MSD response is.

Lorena, Texas (South of Waco)

I agree 100% with Ted, we must remember we are dealing with 60 year old parts, I have noticed there are different lengths of oil pump drives, don't know why, maybe a running change? as far as MSD if the shaft was to long and the end play was large there would no problems, the cam gear would pull it down to the block, the upper movement does not matter (within reason, well maybe if the engine was run backward it would) LESSON check all things on all engines, I just put together a 428 Ford for my son, the intake valve pockets in the pistons were off about .030 who would think? how about all the drama in the rocker arms? how many timing sets are off ? I sent a block out to be bored and honed to match the pistons however he put the pistons in the order of a Small Block Ford (domes and valve pockets in wrong places) so matching the pistons to the bore was useless.

Cliff Murray

PS This is a good place to share ideas   

Bass at MSD has referred this to R&D, I think it's a way of putting me off and maybe I'll go away.

Cliff

PS https://performanceparts.ford.com/download/pdfs/DistributorGearInstallation.pdf

An idea for Ted and Cliff for your performance builds.
Why not machine the gear or block for a thrust bearing. Eliminate the friction of the gear riding against a bushing or the block.  We do this with our racing power glides.
Ray Barton built an oil pump for the hemi Stock/SS engines that had the oil pump drive gear supported on both ends by a bearing and a thrust bearing for the drive gear to run against.
It would be interesting if done for the Y.
It was expensive to buy but was an interesting piece, and showed out of the box thinking. 
Unfortunately he has stopped producing them.
Dave

Well a little more trouble, these heads have push rod tubes installed in the lower ports, 2 push rods rub on the tubes, so apart again
(I may try to rat tail file them on the engine)

I thought of something else regarding the distributor gear/block juncture.  Maybe I should stop thinking.  Anyway, why would Ford spend the time and money to spot face the block and machine the bottom of the gear if they didn't intend for them to rub?  Then they put the rocker arm drain tube back there to flood the area with lubricating, cooling oil.  Have any of you guys who pressurize your rocker shafts noticed any distress in the block and on the gear?  Jus' wonderin'.

John - "The Hoosier Hurricane"

Good question. I’m still running the original 55 tach drive dist. in my 55 bird. It’s been rebuilt, probably 8000 or so miles ago. I had a lifter failure (#1 exhaust, head fractured into 3 pieces. Took out the cam, no wear on any other lobe or lifter. I think it was a fluke). We went over the engine real close before a complete rebuild, and there was no sign of galling on that surfaces. All those miles were with either a set of Mummert’s ported 113 heads or the aluminum ones, both using pressurized rockers. Just a drilled orifice no factory tubes.

The distributor is locked out, the computer controls the timing, before someone jumps on me.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Hi, working all morning, I've been running a reamer through the sleeved push rod tube to get enough clearance for the push rod, been doing it by hand, I don't want to break through the sleeve, the mill would have been quick but if I went through big problem, I taking a break for a soda, here's the 428 I just built for my son, it's going into a 1957 Fairlane  500      

Going home, worked like a horse, push rods still rub, grind and check over and over all morning.

What's with the trim on the engine vs the choice of distributor? I mean i run a lot of those mallorys but i would never dream of doing it on a motor running those valve covers. I cant imagine that is the best distributor for a modern dressed engine like that