cab swap

[seafoam68]

Hey guys, discovered something different about my cabs. I want to put a '81 c-30 cab/clip on a '80 c-30 frame. (The 81 is is much better shape than the '80) What I noticed is the '81 is an automatic truck with a "low" hump floor and the '80 is a 4 speed cab with a very high hump. Question is, why the increadiable difference, and will I be able to use the "auto" cab with the smallblock/4 speed combo on the '80 frame. I had planned to merely cut a hole in the flloorboard for the shifter, but now I don't know if the trans will fit under the low hump floor. Anybody done this ? Thanks.