Doing this right now on a 68 El Camino. Same principles and parts as drum brake first gen Camaro.
I bought a disc brake booster and mc for ridiculous cheap on CL. Brand new MC with lifetime warranty. The guy put it on his 68 Chevelle and his fancy wheels wouldn't fit, so he bought a complete Wilwood kit.
Cheap Big Brakes
Very straight forward following the guidlelines set out on David P's web site.
Wanted to ad that you will need to source a new bolt for the top of the bracket. The drum brake bolt doubles as the anchor pin for the drum brakes.
Also wanted to ad that if you find a set of backing plates cheap (I did.... they came with the used 69 style caliper brackets I am modifying... paid $80 free shipping for caliper brackets AND backing plates) you can use the 69 Camaro or Chevelle dust shield. You just need to make a lot of cuts along the perimiter to flatten it out just a bit. If you aren't worried about looks (who is going to see your dust shield anyway?) it works just fine.
One other thing; I didn't see this in the write up, but just to make sure everything fit perfectly, I had the "additional" metal drilled an bolted to the spindle before tacking the caliper bracket in place. Then took it back to the bench to make sure everything was square and lined up perfectly. I didn't want to have to wallow out the bolt holes even a little bit. Everything fits tightly that way.
Also, when you order calipers and brake hoses, don't forget to order two banjo bolts (I didn, so now I have to wait a few days to get this on the road).
Now, if I can just find someone with a mid 70's Buick or Olds with 11 inch rear drums they are parting out..... I would be set. Plan to use the El Camino as a tow vehicle from time to time, so that is why I went with the Corvette front rotor and truck calipers.
MANY THANKS TO DAVID POZZI FOR POSTING THIS PROCEDURE. I will have less than 1/3 of the cost of aftermarket brakes, and it will be serviceable with all GM parts.
This is a really fun procedure if you can do light fab work and have a good welder. I did not send the spindles to be machined. I measured carefully and cut it with a hack saw, cleaned it up with a large file. Hey, I needed the exercise anyway, and this is better than the gym. Plan on wearing out a good Lenox hack saw blade per side before it is all said and done.