Either manifold will work fine, I've installed both of them and had no problems with either of them. Are you using a GMPP manifold by Edelbrock from SD ? If so everything will swap over fine and you won't feel much difference from the original vortec intake. As far as the 96 running rich it's possibly a stuck injector poppet. I ran into that quite often. If you can get someone to scan the PCM it will tell you if it's an O2 or not. You won't want top use the vortec distibutor with the TBI intake make sure and use the one that came with the TBI.