Carb pondering

[jdhcth]

I have a 67 LWB with a 283, 3spd, fairly beefy cam, Edelbrock performer Intake and a Holley 4175 Qjet replacement 650cfm carb. I get 10MPG. I want to improve this. If I go with an Edelbrock 1400 or 1406 will I improve my MPG and/or will my performance suffer? Also, is a 650cfm too much carb? Iv'e used some Online calculators and they tell me 500cfm.

I also have one of these early 60s GM 4MV's layin' around, would it be worth it to rebuilt or have this rebuilt?

Thanks,

JD