For what it's worth, the 231 odd-fire uses the large bore 2GC while the 225 uses the small bore. At least my 1977 231 odd fire has the large bore carb. I think that is the case for all of the 231 manifolds. I'm curious why the Holley won't work on an odd fire. It's not like the throttle body injection is SEFI where it's timing the injectors with the individual valve openings. I wonder if the uneven pulses for the tach signal are a problem? If so, an independent crank trigger of some sort might be a solution.