But what kind of driving habits are we talking about here?
You know the old man in the funny hat puttering along like he's gonna live forever? Drive just like that guy!
It takes some mental re-training to drive for mileage, but once you are there, it's kind of fun. Then you can be a bit smug, and make fun of Prius drivers for dropping a fortune on their trendy disposables, while you get close to the same actual mileage.
I don't drive for mileage in the Corvair, there is a some space between idle and WOT, but it rarely sees that area, just too much fun.
The 1946 is a very nice 1bbl carb. 5200 a very nice 2bbl carb.
The 1946 was designed to sit on a 200, and extract the best mileage possible, at the time. There isn't that much that needs adjusting on one out of the box.
A 5200 will need some tuning, experimenting, and probably some jets, but I can't see that one or the other, once -
properly- set up, would be more efficient.
The "problem" with a 5200 is that is has more headroom. You are far more likely to stomp on it if you know it will do more than just change the way the engine sounds...
Rick(wrench)