I just looked at the one I took apart and the 1:1 scale model right next to it, and I don't see that connector. It might be different on for the El Camino. I bet it is since the compressor is on passenger side in the NA G-bodies.
I believe TRW only makes a standard and .030 over forged piston. Bore size is not going to make a practical difference in power output with the 109. How many miles are on the engine you are rebuilding?