350 Pontiacs are a direct bolt in and relatively cheap and plentiful as long as you are not looking for a particular "numbers" engine. 400 2bbl from big cars are cheap and common too, and come with a TH400 in many cases. However, the TH400 will be long tailshaft and will either need the tailshaft and tail housing replaced or the driveshaft shortened and a mount plate extension made.

Because Camaros and Novas shared the subframe, frame mounts are easily found for the Chevy swap. However, you'd need to modify all the wiring as Chevy is set up differently.

I really like the cammer engines, particularly the Sprint. But you are correct in saying that they cost more to build than some other options. 326 engines do as well.

There's not much good to say about emissions era engines except that you won't have anyone else trying to outbid you for one. I've bought a few for transportation specials. They generally have the fuel consumption of a large V-8 and the performance of a small V-6.

If you've ever assembled a mixed-breed car, you already know that it can be a royal pain to visit an auto parts store and buy an alternator for a '76 Chevy, a brake kit for a '68 Firebird, a rear axle cover gasket for a '79 Trans Am...and so on. You almost need to carry a glove box index of your car. Stick with one make for easiest fit and maintenance.