Double Plane Intake

My 408 with an Airgap dual plane made 504 hp, but we didn't do a low rpm pull so I can't verify the 2,000 rpm and up torque. BUT, a dual plane helps with reversion because it has longer runners, cutting down reversion sooner than a single plane. Try a Duel plane, along with 20 degrees initial timing (cut back the mechanical advance too!) And check the cam installed position. You could go four degrees earlier than the cam maker recommends to see how it works. Leave the gears, but if your converter is tighter than about 2600 to 2800 stall, a move to a 3,000 or so stall minimum will help a great deal. If all this doesn't satisfy you, time for a cam change.