On the carburetor jetting issue I suggest you give George Asche a call. He is the carburetor king on Mopar flatheads. He does not do internet so a phone call would be in order. He can be reached at (814) 354-2621.
He is running three carburetors on his 29 Desoto powered by a 265CI flathead as pictured below. The second picture is a Dodge I saw while visiting George. It has a 265 bored to 283CI.
