I know I will get in trouble for saying this, but here goes.  I have no doubt it is possible to build a Y Block that will live at 7,000 RPM.  Y Block parts are expensive.  I have $5K in my motor and it's basically stock.  If I blow up a modern engine, no big deal.  I order new parts from Summit or Jegs. If I blow up my Y Block I may not be able to find a replacement. 

I own a Y Block because it brings back memories, not because it revs to 7,000 rpm.  The sound the starter makes when I crank it,  the burble from the dual exhaust, the oil dripping on the floor of my garage and the feel I get when I grab second gear.  Everything about my Y Block brings me back to the early sixties when I was working for $1.25 a hour bagging groceries.   Back then I drove like a crazy person.  I broke transmissions.  I broke differentials.  I bought engines for $50 and blew them up in three days.   If you want to know the upper rpm limit of a Y Block, it's not hard to find.

The question is not how high you can rev a Y Block, it's how many do you want to buy?

The little 303Y block for EMC this year was dyno tested from 4100-7100 rpms, and has 52 dyno pulls on it so far.  Ford crankshaft, 113 heads, .591" lift camshaft.  There is a lot of work involved, but the crankshaft and heads do not seem to be a hinderance to rpm.  Any well prepared/rebuilt 292/312 should be capable of 6500 rpm with a camshaft that is ground for the purpose.  The Y Block is a strong platform that responds remarkably well to performance upgrades, in my opinion.  We made 390 lbft torque, and 453 hp with iron heads, 10.4:1 compression, and 303 cubic inches.   Joe-JDC

JDC

Personally, I would never take a stock YBlock over 5,500 rpm.  The weak link are the heads and the push rods may as well be made out of spaghetti.  My motor has "G" heads, tubular push rods, ARP rod bolts and it has been balanced.  It also has an 301333 Isky cam. I don't think it would make any more power at 7,000 rpm even if it hung together.  Maybe if I had aluminum heads, headers and a better intake?  Even then, I wouldn't chance it.

I do not drive my '56 Third 312 aggressively but out of curiosity, is there a "redline" rpm? The factory 5000 rpm tachometer has no such markings.
Jim Yergin