toomanytoyz did it the same way.
you can cut the one ton frame a bit long behind the cab, remove the rear cab mounts from the 1 ton frame, cut the 1/2 ton frame in front of the rear cab mounts, bolt up the 1/2 ton cab mounts to the cab then bolt and/or weld the frames together after you are sure you have them parallel, square, and level. pretty simple and the cab mounts help align the rear frame section
Here is a couple pics of toomanytoyz' frame
