I know your str8 6 has an aftermarket intake, but the aftermarket intakes were designed to use the stock carbs which could ither be a rochester carb, or what you have, Carter W1's. is the idle circut removed from 1 of the carbs? if not, that's part of your problem. The Holley/Webber 5200's from langdon's are only like $89 each. a 1940 Holley might work, you would need to measure to be shure. the Ford Six crowd uses langdon's 1-2bbl adaptors and his H/W 5200's, and a 1940 Holley should also bolt up, a parts store should be able to tell.