Increase in gas milage

[Awann99]

My 69 gmc 1500 Long bed. Leafs in the rear. 307 rear end. Year old 350 crate. Quadrajet Th350gets around 12-14mpg. If I switched out the quadrajet for a Holley sniper. Installed a 700r4 different rear end gearing. Probably 3.54. What kind of fuel milage increase would i probably see. I would like to trip in to the goodguys get down next year without killing my wallet in the process. I do not want to LS swap the truck. Any other ideas to increase the gas milage? I also would like to make it be my daily for college (because who wouldn’t love daily driving a c10 ) but the few times I have Commuted in it the gas was too much to keep up with.