@95silverado, are you 100% going the disc conversion route and no longer in need of replacement drum backing plates? A trip to the yard may happen this weekend but I’d rather not mess with trying to score those if they are no longer needed.
Also, since I have some interest in a rear disc swap I’m really interested in seeing this play out if you go this direction. Are you planning to purchase the lugnut brackets then modify to provide better caliper support?
From what I’ve found, the 3500 DRW Express/Silverado/Sierra use the same rotor and the backing plate crosses between them. Your chart shows the calipers with dual 2” pistons but when you look under the trucks there are also dual 2.4” piston calipers available.
To me, assuming the math works out with the caliper bore sizes, this is a better option. You would have a more robust caliper mount and a better designed parking brake with the internal drum vs the ratchet/screw style from the Caddy. Welding the replacement axle flange onto the axle tube should be pretty straightforward using the brake assembly to set proper spacing and getting everything square.
This would be my preferred method of making the swap, so really curious if you already considered and found a reason to rule it out?