i have a 1966 c10 that the man i bought it from hot roded with a 305 and a 350 turbomatic transmission and a 4:10 geared rear end. what can i do that will help this truck get better gas mileage. If i put in higher gears like 3:75 would it make it better. I had also thought about getting an inline six to put in it how much better gas mileage would it get.

thanks.