Ted, how steady is the timing? Getting rid of any spark scatter may offer some Hp. Also on the air pan, I use a moroso dropped aircleaner base pop riveted to my airpan and sealed with silicon. Decided on that after working with a 383 that we tried a flat pan on, gained significant power with a better entry system. If you have a flush machined carb top (choke towers cut off)there is a cast piece that can be mounted to round out the air entry, forget who makes them.
Have you done a full graph on the front end for Bump steer? Needs to be with in 1/8 total top to bottom. Rear axle alignment? To be sure the rears are parallel. How are the brakes? Nice and lose?