I notice that you're presently using a square-bore double pumper carb on a spread-bore Performer intake, so I guess you must be using an adapter plate. I'm no expert on the subject, but I've never liked adapter plates. I've always felt they cause poor fuel distribution and rough running. Wouldn't it be easier to try a spread-bore carb on the Performer intake before going to the trouble of switching to the Performer RPM?