RPM AIR-GAP carb spacer?

I was wondering if any one had a suggestion on wich carb spacer works best for a rpm air-gap intake on a .030 over 360 with 10.65 to one compresion? I am running a 750 holley double pumper with a pro-form center section. The car is a 72 dart that runs 12.30s @ 108mph 1.68 60 ft. It also has a 4000 stall converter with a 4.10 gear! I'm just looking for a little extra and would love to get car in the 11.s Any advice would be helpfull!