Six speed for Jim

Hey all,

This is my first post, just signed up today. I need some advice on a transmission swap. Ive got a 1969 GMC (Jim) SWB fleet side pickup. The truck has a six cylinder with a three speed manual transmission that shifts on the column. My plan is to swap out the six banger for an LS1 from a late model Z28. I know about swapping the electronics that go with the engine, so that's not the issue. What is giving me some concern is that I would really like to keep the truck as a manual shift,  not with that old three speed, but with the six speed that the LS1 is hooked to. Ive done engine-tranny swaps and have dealt with cross member and drive shaft issues before. Those are easy enough to remedy, but Ive never had my hands on one of these transmissions. So I guess what Im asking is, am I stepping off in something that will be nothing but heartaches and frustration, or is it a RELATIVELY simple task? Any advised would be greatly appreciated. Thanks in advance.