Just my $.02 worth, but remember there are additional differences in the frame and suspension between the 1/2 and 3/4 ton pickups.
For example the 1/2 ton frame is wider at the rear than the 3/4 ton. As a sanity check you might want to take a look at the factory assembly manual which provides detailed specs and measurements. IMHO you would be better off buying a 1/2 ton rolling chasis and swaping the sheetmetal.
JimBo
