1. The Current value and does changing things hurt that value. 2. The cost or bang for the buck 3. Reliabilty - how you drive 4. Goal of the car. Sunday driver, weekend worrior, show car, fix up and sell ect..
To me I would just see at as a 350 car and I would not be to worried about ruining the value by changing the engine, although I'm only talking about changing it with another pontiac engine not a chevy. I'm not a fan of chevy swaps at all although I have considered an LS1. Since rebuilding a engine is pretty much the same cost no matter what you build I would base the engine on what ever my goal is. For me it was power so I have a 455 in mine. My suggestion would be put in a 400, use all the bracket and pulleys from the 350 and maybe even the heads depending on what they are. You would get more power and just as good of gas milage if not better. A Buttler engine would be great or find a good engine builder that know pontiacs to build you one. my .02
