[Elbert]

I would use the transmission that's connected to the LT1. You need to get a larger radiator for sure. Better take some good pictures and notes if you are not familar with the engine in the car. I would suggest you buy a shop manual that matches the 94 caprice so you will have some reference points.

Don't the LT1 engines run electric fans and have no provision for a fan clutch? If that's true then you might could swap the electric fans off the car on to your truck after you get a 3 or 4 core radiator designed for a V-8 C-10.

I'm guessing the motor mounts are configured differently on your truck for the V-6 as they would be for a V-8. Find a buddy with the same or similar year model pickup with a V-8 and get the motor mounts and install them like the reference truck. You will also have to figure out how to get an electric fuel pump setup correctly with the correct pressure to feed the LT1.

Get all the crap off the doner car, and I mean everything under the hood. Get a digital camera and take a bunch of pictures. Most of the wiring harness have plugs that can only work one way. Get some tape and mark the wires so you know where they go.

Don't skimp on the right radiator.... the one out of the car might work?