MaSnaka John You are asking alot with a semi stock 390 motor. We have no camshaft spec, no head work done, IMO a large carb on a small motor. It sounds like the cams shaft is stock and a hydro lifter motor. 5,000 is about the limit on a stock cam shaft. All you need is a 650 Holley on this motor. Forget the double pumper. What valve springs are on the heads? Has the heads had a rebuild? We don't even know what compression you are running at? It sounds like you built a torquer motor. I don't know where you live but if there are cold mornings and you want to go for a drive, A choke is a nice thing to have. This is a street car, not race. As for the side pipes, the only way you are going to know if they are hurting the motor is with a back pressure gauge. At WOT you want to see 1.5-3.0 psi on the gauge. Anything more and you have a back pressure issue with the pipes. SOME motors like a higher number in back pressure than others. 5.0 psi would be my limit on any exhaust system. It's all about matching the parts. The best thing I can offer for ideas is to replace the heads with a set of KCR heads stage 2, gasket match the intake to the heads, get a sheet for this camshaft and see what we have, and go a little bigger with some thing in the .500"-.550" with a 112 LSA. This will be a hydro lifter camshaft. REMEMBER, TORQUE moves the car not HP. You are looking for a big fat torque curve from 1,700- 4,000 rpms. Your drive train will take on the high side about 20% of your power with everything hooked up. Depending on air filter base it can help bend the air into the carb. There are 10-15 FE motor builds over the years for 390-428 motors, follow the Edelbrock 390 builtup. You will be very happy for a starter motor. After this, it's stroker TIME and BIGGER.
Rick L.