Super Six Jet Size recommendation

I was hoping I could get a recommendation for a jet size that will be suitable for a daily driver. I currently have a rebuilt 1971 - 225/6 bored 30 over with stock cam , a Carter BBD and 2&1/4 exhaust pipe with stock Walker muffler.. The motor is broken in already. It is getting poor gas mileage - approx 14 mpg. I have the stock Holley 2bbl carb for this motor (new) and was looking replace the BBD with it. I was hoping to increase mpg without losing too much in performance. Any input on a jet size is appreciated.
Thanks,
grasshopper