I bought a rebuilt Q-Jet from the NAPA store when I converted from a 2bbl. I am amazed how well the thing runs without any trouble. It just happened to come in with a 1970 Pontiac casting number. It was rebuilt by Tomko I think. Cliff Ruggles says such rebuilts should be avoided because they use parts from different carburetors in the same carb. I respect Cliff but I guess I got lucky, and maybe it's just because of the inherent quality of design in the Quadrajet.