Need recommendation for a Carb for better MPG!

Just my 2 cents.

Look for a metering rod that is slightly large on the fat part and same diameter on thin part. That will help lean out the carb in high vacuum situations. Run it lean and if running a cvac adv distributor get the timing up. Make sure it doesn't surge or feel like it's straining at cruise.

If you have access to an AFR meter, even better to try and get the numbers up at cruise. At least you'd know if it was getting outside of 15.5-16 or so.