I'm not sure that a modified original manifold, or same with adapter using a 2 bbl. will have the same cylinder-to-cylinder mixture distribution as stock.
This is also true of the 2 X 1 manifolds: most including Edelbrock, Offenhauser etc. have the carbs centered in the inter-port distance, but others including Fenton have the position biased to the end cylinders. I suspect the latter is a better choice.
If choosing carbs or a manifold for 2 X 1, the size you want has the SAE #2 2-11/16" bolt pattern. The SAE #3 2-15/16" pattern is best for larger engines and higher RPM.
