true from what I know as well 96 and up was vortec, usually have vortec on the valve covers, and they have a saw blade kinda casting mark on the front of pass head.
I also hear that the tbi heads are good for low end torque, you had 305's and 350's tbi's as well.
Definately need an intake for vortec heads and need an aftermarket one, cheapest I've seen has been around $150 or so.
Now I aint sure, because I never done it but, I think the tbi heads will work with the stock intake if you oblong or elongate the 4 center manifolds bolt holes since they are a different angle then the old style heads.