On the 10 bolt. I know a couple here locally that has a 69 Chevelle with a ZZ 383 Chev crate engine, 3000 stall, turbo 350, and ET streets for tires. They have a 10 bolt rear with an Eaton possi, 410 ratio, and stock axles. The rear suspension includes a U bolt ladder system, good shocks, and hard bushings. Now it would seem that he is on the edge of blowing this rear end, but he has bracket raced it a lot for three plus years.
The quadrajet and stock manifold may not be as restricting as you think, depending on the year. The early ones seem better the the smog years. It is heavy though. There are books you can buy on performance tuning that carb that can really add to its performance. Create good traction and a good holeshot then add hp.