I was really close to getting it, but I gave up. I had a dually back plate from a 90's 1 ton, and a drum and brake hardware from a 90's 3/4 ton single wheel. The deeper dually back plate in combination with the 13"x2.5" single wheel brakes allowed the 14bolt brakes and drum to fit on my '49 dually HO72.
I ran into issues when I assembled the brake shoes. The dually back plate is expecting 3.5" wide shoes, so the 2.5" shoes sat crooked because they didn't reach the spot they are supposed to ride on in the back plate. So the top of the shoes by the wheel cylinder were out at the right distance, but the bottom of the shoes by the self adjuster were at an angle back in towards the back plate. They are supposed to be parallel to the back plate but aren't.
I thought of welding on a spacer or doing something with a flat carriage bolt but figured that might create an opportunity for the shoes to get hung up on something. If someone wanted to get creative they can probably create a shim or guide plate to go on either the shoes or the back plate. I still think it might be possible, although not too practical especially with the rear disk kits that they have now.
Lessons learned:
New back plates don't come with the brake shoe anchor pin. That's the thing near the wheel cylinder that the shoes rest on, and the various return springs attach to. They are not carried by the common supply houses. I finally found some at wholesalegmpartsonline.com
The brake hardware kit, and self adjuster repair kits, while complete and inexpensive - do not have the parking brake lever. That's the part that attaches to the rear shoe and gets pulled on by the park brake cable to actually set the brake. Also not carried by the common supply houses, but found some at wholesalegmpartsonline.com/
You'll also need brake shoe guide plates (which go on the brake shoe anchor pin), and a brake bar lever, which goes from the park brake lever to the front shoe.
Wheel cylinders don't come with the brake shoe push rod/push pin. Got some of those at Napa, I don't have the part number handy though.
The rear park brake cable (the last run that goes from the frame and into the drum) will need to be figured out. The newer drums have the round hole where the conduit snaps in and is held on by metal spring tabs, where as the older ones have the metal plate with two screws that hold the conduit to the back plate. I found a cable that looked like it was going to work. It was the right length for both the cable and conduit. I ground off a ferrule to get the right amount of travel. It fit in the drum and connected up to the park brake lever. It might have worked, but I was figuring that out around the time decided to give up.
Here are the part numbers, all from RockAuto unless otherwise noted:
Back plate: GM GENUINE 15622343 (left side, I never ordered a right side. Only difference is where the hole for the park brake cable goes. Single wheel plate has 2 holes, one with a rubber plug, not side specfic)
Drum: ACDELCO 18B111
Shoes: POWER STOP 451R
Brake hardware: ACDELCO 18K561
Self adjuster kit: ACDELCO 18K39
Parking brake cable: RAYBESTOS BC95182
Brake shoe guide plates: DORMAN 13896 Drum Brake Shoe Guide
Brake bar lever: DORMAN 21152 {#3898059} Brake Bar Lever
Brake shoe anchor pin: GM 14009982 (wholesalegmpartsonline.com)
Parking brake lever: left - GM 15649193, right GM 15594177 (wholesalegmpartsonline.com)
It was a fun experiment though. I learned a ton about drum brakes and found that wholesale GM parts website. If I ever have a 1960s+ truck(or whenever they settled on the self adjuster brake design) I'm good to go with the drum brakes.
I used this Youtube video to help me figure out assembly. The guy had a good trick for assembling the self adjuster spring in a vice rather than trying to do it on the truck. It worked like a charm.
https://www.youtube.com/watch?v=0tRmf1zd7XQ
