cutting the frame is not for the timid. I would box the frame if you do cut it. My truck is a totally different animal, but same theory.
what if.......
you mounted the cab back a little bit and the bed back a little bit more for a bigger gab between the cab and bed? just an idea

1953 Chevrolet 3600
Fried Green T'mater (Vern)
In the Stovebolt Gallery
Caution: Political Statement
Man who runs in front of car gets tired, man who runs behind car gets exhausted.