The Holley #7448 350 CFM 2-barrel is a good choice for engines the size of the 250. They're available through JEGS, and various other internet/mail order suppliers. We use them on the NASCAR round track engines instead of restrictor plates, on the low-budget "claimer" engines. A properly set-up Chevy 350 will run 6,200 RPM with one of these carbs, so a 250 I-6 definitely won't be under-carbureted with one installed! Holley also makes some low-volume 4-barrels if you've just gotta have four holes to breathe through, but a 4-BBL on an I-6 is a waste of time and money, IMHO!
Jerry
