I removed a 6 cylinder and 3 speed column shift from a '63 1/2 ton and replaced it with a '67 283 V8 out of a Chevelle and a '65 4 speed from a 1/2 ton. I was able to buy the whole truck (the '65) for next to nothing (this was about 20 years ago). To make a long story short, the floor panel was a perfect fit. That is one of the things I like most about Chevy's is how interchangable the parts are. If I were you, I would look for both the floor panel and tranny at the same time. I would bet that the floor panel is probably different for the Task Force years and may be tougher to find. Unless you don't mind fabricating something.
The first thing I would do is try to find another '59 or 58 to look at.
