I am working on a 53 3/4 ton truck. The wider rear may or may not fit depending on the wheels you plan to use. 2.5" is not too much to overcome with a reversed wheel, or deeper backspacing. Another solution, if you need to replace the fenders, is to use the 3" wider fenders that are available for these trucks.
For mounting, the 1/2 ton frames have a significant kick-up right above the axle, this allows adequate travel between the top of the axle and the bottom of the frame. It also lowers the truck's rear. I 'flipped' the 12 bolt GM truck rear end I put under my 53 to the top of the springs to lower the truck. This also means that I had to notch the frame to provide adequate travel.
