Seein' as how you asked:
Not an exact match.
You will run into problems if you try to hybridize two different era vehicles--doable, but a lot of work.
Using the later cab, if 1979 or newer, has gas tank under the floor, different dash, bolt-down hardtop-to-cab, raised floor from under the seats on back, different door latching on B-pillar jambs, etc..
So, depending on the size of the repairs, grafting the floors from the newer one to the older one is problematic.
Would you be rehooking-up a dash-mounted transfer lever?
Have you measured tunnel outlets for the shifter(s)?
Not sure that all the cab mounts are exactly in the same spots.
Etc..
Seems like less problems to carefully cut-out and weld-in matching patch panels to the rotten floors. Could be made to look original with careful and skilled work.
Or..........go commando and create a truck with as much of the later era pieces as you can muster.
That, however, requires coming up with a lot of different parts, and depends upon just how authentic you want the results to appear.
If the floors are the only thing wrong with the older cab, I would personally fix them, and sell the newer cab to someone who either needs a later-version cab replacement, or has the time, money, and desire to create a later version truck.
Just my two cents. Make that one cent, with our new economy.
