WELCOME to the Stovebolt
If those trucks were mine I wouldn't be using either one as a parts donor, they are way to complete to do that to them. If you need parts place a "want ad" in the Swap Meet section.
Installing a modern engine, trans and rear are done all the time, then add disc brakes to your original front axle and your set.
There's a member here that sells front disc brakes kits for the big trucks.
Mike B
