I'd tune what you have, you are still leaving some on the table. For example, my 318 duster ran 9.5's at 74 mph with 2.76 gears, stock converter, no headers, 318 heads and stock bottom end and less compression than a factory A L318 because of the thick head gaskets. I'm not stating "mines" good, I'm stating "yours should be better", especially with 3.91's.