You're in for a *lot* of work.
Obviously, you'll need to convert the truck to 12 volt, if it hasn't already been done. The only reservation I have with your proposed setup is the transmission. The T-56 6 speeds that come in the late model Camaro/Firebird/Corvettes are great transmissions, but they are *huge*, so you might have to modify your transmission hump some. Plus, you'll have to add some sort of computer to control them. (yes, the manual transmission has a computer controlling it.. heh). A late model LT1 350+ T-56 setup complete with clutch and computer out of a F or Y body car can be found for about $3500-4000 give or take depending on miles/condition.
If it were me, I'd get a regular 1st generation 350 block(1967-1999) with a 4 or 5 speed non computer controlled transmission. I think that would be far easier in the long run. Besides, you really don't need 2 overdrives for this big ol truck, do you? They're meant to haul loads.. not go fast.
I would think that you could pick up a good small block engine + 4 or 5 speed transmission *much* cheaper, and still have a great driver.
I've got the T56 in my Firebird and I feel that it is a great transmission for a sports car, but it simply is not geared for a truck application. But, if all you do is drive the truck on the highway, and rarely use it to haul stuff, you should be just fine.
Good luck with whatever you decide
Chris
