403 Olds or 350 Pontiac?

My '78 Trans Am is an original W72 car but when I bought it someone has swapped a 403 into it. I'm currently resto-modding it pro-touring style and as with most projects, I bought a parts car. The parts car has the 350 HO motor in it. My plan is to swap a modestly built LS2 into it but I really want to hurry up and get it running so to save time I plan to fit my subframe for an LS series motor and run either the 350 or the 403 until I get the LS motor built. My question is this: What are the pros and cons of each engines and which would you use if it were your car?