rochester/carter 2bbl carb bolt patterns

WHICH Carter and WHICH Rochester? There are more than one of each. The 2 main Rochester two barrel bolt patterns that everyone calls the small (3 1/4" x 1 7/8") and large (3 1/4" x 2"). Those are the 2G and 2GC respectively, I believe. I just went out and measured the bolt pattern on my Carter BBD and it does appear to match the smaller 3 1/4" x 1 7/8" of the smaller Rochester.