Yeah. Looks like I can get a power dual master now and hook it up to the drums to drive around until it snows. Then disc kit this winter and add a proportioning valve.

Sounds like a good Plan. At least if You buy a KIt everything is new and Spindles are already Machined so it's basically install and go.

  

Thanks for all the replies guys. After looking at piecing the kit together more, I'll probably just do a kit this winter. No racing or anything crazy, but it is a family car, and we live near Chicago, and some people drive like assholes, so being able to stop quickly is a must sometimes. And next summer or winter I'd like to try to get an old canned ham camper to fix up and pull with the car. Figure discs would be pretty important to work with that.

I worked with Dave Gully owner of Drop em Stop em.  Put disc brake kit with 1 1/2 drop spindals my 1954 Ranch Wagon The guy is great. Customer service and follow up questions answered ASAP
Dave may still be able to line you up with a bolt in 8" rear end
 https://www.jalopyjournal.com/forum/threads/dropem-stopem.679020/

I think brake choice is all relevant to how and where you plan on driving. I have both drum and disc type cars. This is some of the observations I have made over the years.
1. I had two 1966 Mustangs, one disc one drum. Under normal driving and good weather the drums worked fine. Under extreme hard braking from 70 mph they faded and after two stops in a row the braking was almost gone completely.. Driving in heavy rain, puddles etc nothing is more fun then wet drum brakes. The discs never had these issues so I have to give the Disc a +. I kept the one with discs and gave the drum one to my son who later converted it.
2. My 1960 F100 that I built in 1975 still has drum brakes. This truck has been driven in a lot of mountain type roads on many road trips across the country over the years and worked great when we had good brake shoes, I always used Grey-Rock semi metallics. But things have changed, I don't know what material they are using today ( I'm assuming recycled cardboard ) Around town they are OK but the last trip I made to NM, 2000 miles round trip was a little scary..
3. My 57 Ranchero is now converted to disc/drum only because I drive it hard on mountain roads, I'm still some what of a road racer at heart. If I was only driving it locally around town I would have left it drums.

The rears can be converted to self adjusting. I did it on my wagon.

Durham Missouri

Add a vacuum booster and be happy. If your planning on driving 15-20k miles a year maybe, but I'm not changing my stock drums and haven't seen the need and January will be 6 years. Your still going to adjust the rears since they won't have self adjuster either. I adjust all 4 on an oil change just like the 50-60's.
If your going to modernize everything then it probably a good thought, I'm still contemplating AC and haven't done that either, but I live by the west coast and would need that only a few times a year... Drive and have fun with your Merc especially fixing all the little stuff you mentioned...good luck.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

While I agree that Disc brakes are far superior in braking than Drums. I grew up driving the cars with Drum brakes & had no problems whatsoever,  and the drums with Power Brakes were just great to me !   And to me,  it is a matter of keeping our classic cars original as much as we can !!   Keep em like they were !!!!  Whenever I go to car shows etc it is the origjnal cars that I am drawn to, even if they have some hot rodding stuff from that time period !!!!

Respectfully disagree. I can tell You from Experience that the difference between 4 wheel Drum and Disc/Drum is MUCH better with the Disc.The north American Car Makers were a long way behind the Europeans when it came to improvement in the Brakes. Would You also say that Dual Master Cylinders were not an Improvement in Safety? Everyone is entitled to their Opinion.

  

Unless you plan to road race your Mercury disk brakes are a waste of money (Not to mention the fact that they take away from stock and lower the cars' value) Drum brakes have more sweep area than disks so they stop faster. Disk brakes were put on cars because they are cheaper in parts and labor on the assembly line, if you look in the original advertising from the 60s the auto companies never said they stop faster (Except when overheated) or better, they just implied it.