Slow, Driving Rustoration 1972 Dart

Got the carb rebuilt, all of the ECS hooked up, the transmission cooler installed, transmission cleared of most if not all contaminated fluid (it took 8 quarts to fill it) and took it for a 120 mile round trip. It ran perfectly, smooth idle, great acceleration, no stumble or hesitation on acceleration, and the cabin didn't smell as much like gas fumes.

Next up on the upgrades and fixes will be the exhaust, it has leaks where the manifold pipes join together for single exhaust. Even with the floors all sealed up I'm sure I'm getting some fumes in the car. I may get a quote on it, or maybe order a dual exhaust kit.

I'm also looking at putting a 4 barrel intake and a 500 cfm carb. I'm just looking to get better gas mileage. From what I've read here it looks like a SP2P is a good choice and a edelbrock something 500. Do I need headers for better MPG or are stock 318 manifolds good enough? Good enough being relative. That said if I found a cheap set of 340 manifolds I'd swap them in a heartbeat.