CrewCab Frame question (1/2T vs 3/4 T)??????

[Hart_Rod]

I'm trying to figure out the best way to build a frame for my 4 Door CrewCab. It is currently sitting on a 3/4 Ton LWB chassis. I've purchased a completely redone SWB 1/2 Ton chassis. I see my options as:

1. Shorten the 3/4 Ton frame and transfer all the parts over from the 1/2 Ton.
2. Cut the rear clip off of the 1/2 Ton and graft it on to the 3/4 Ton and transfer the front suspension from the 1/2 T frame.
3. Cut the extended portion out of the 3/4 Ton frame, then split the 1/2 Ton frame and graft in the 3/4 Ton section.
4. Split the 1/2 Ton frame, find another donor frame for donor rails and make it match the original 3/4 ton frame (as far as where the cab mounts).

I'm leaning towards #4. Any one else got any ideas? Also, why is there a difference in the 1/2 and 3/4 Ton cab mount bushings? Are the mounts the same and just the bushings different? Thanks.