Is that the engine your putting in??..if so that looks like an Air Gap I'd stay with it and see what it runs..my duster with the 416 ran 11.02@121 with an Air Gap:D:D
That is a Chinese airgap that is gone now. I have an opportunity to pick up a MP M1 for rectangular port heads. I am gonna have Dominic with Thumper Carbs build my ca .