Just a thought (and maybe a dumb idea full of holes).
If the Vortec 350 is running, I assume it has a good fuel injection system and computer. Have you considered putting the complete fuel injected Vortec in your truck? It may be simpler than going through all the changes you need to get a Vortec working with a carburetor. And it will probably run as reliably as a stock engine.
You will need to figure out a fuel pump that works, and you will need a VSS and O2 sensors to feed the computer. The rest of the sensors should be on the engine. I'm also not sure how the computer would work with a non-computer transmission, but there should be a solution.