The vortec heads are a natural swap for the TPI motors, but the problem with bolting them on is that the vortec heads have a different intake bolt pattern than the older style heads, which makes the baseplate un-useable. Even if you were to modify it with a carbide bit to match up bolt hole wise the ports on the vortec heads are so much bigger that they actually rise up over the lip of the baseplate far enough to stick the end of a pen through. The solution to this is offered by Soggin Dickey Performance Parts.
www.SDPC2000.com who have taken it upon themselves to custom design a baseplate to make this possible. designed spesificly for vortec heads and TPI it has larger runners and is worth more hp by its self. Right now i think the price is just under 400 dollars.
Vortec heads are plentiful at the junkyards across the country. Find any 1996-2000 CK platform truck (Silverado, Tahoe, Suburban and GMC equivilents) with the R code 350 engine. Pull the valve cover and check for the head casting number in the rocker valley, you want the heads with the 8? digit code ending in 062. The head castings ending in 908 have pressed in steel exhaust valve seats that limit flow and port modifications. The heads also have a max lift potential of around .480in lift. meaning a mild cam will have to be used, unless you have them machined for more lift. This is a pretty easy machine job that most shops are probly quite adept at by this point. it requires enlarging the spring seats, and cutting down the valve guides for dual springs.
The chambers on the vortecs are a bit larger than those of the stock 350, so a switch to steel shim gaskets would probly be a good idea. but even with slightly lower compression, the heads make more power. The swap to vortecs and the baseplate has been prooven to add 40-50hp to an otherwise stock L98 engine.
as far as cam swaps, it really depends on what the rest of your drivetrain is. you want the cam to match your engine, torque converter, trans, and rear gear ratios. To get a specific cam i would reccomend calling Comp Cams cam help hotline, its toll free, and they are the experts.