That is why swapping baseplates can make your carb a different size. The bores in some models of carbs are the same, it's just the butterflies in the baseplate that are different.
And just to further confuse the issue, there is a single feed, mech secondary Holley, the old 660 centersquirter. And the center hung single feed Holleys were Ford carbs only I think. And there were single feed side hung VS Holleys with metering block on both ends. They just used a longer fuel transfer tube. Used to find these on heavy trucks mostly.
I was wondering about the single hung side hungs... I thought I had seen one, but I know they arent offered these days.
The carb you now have would be worth more sold as is(if it's an O.E Ford Holley), then the money used to buy the smaller carb you want. That carb is a list 80783 650 cfm VS Holley. A 570 SA would also be an excellant choice.
