Did some research on this carb and found out some very interesting data. Seems it's one of, if not the most durable and dependable carbs ever made, and they came in about 5 different flavors! From what I understand, there were two base sizes, the small and the large. The small came in one CFM size (278) while the large came in four sizes (352, 381, 423, and 435 CFM). Aftermarket vendors have capitalized on this durable and dependable carb by gutting it out and turning it into a 500 CFM carb for dirt track racing. Imagine what this carb could do on a small block! The small base was used up to 1971 on everything, while the large was introduced in 1971. By 1973, all Buick engines used the large base. This data might be a bit off, but it's what I found. Tried looking for more specific data on these carbs and only got lost in the jungle. Do a google search and type in "Rochester 2G" in the search box. I've found everything from forum archive discussions to dirt track racing to vendors who sell rebuilt carbs to personal testimonies to old 1950s-60s document data service manuals.