In stock form you will get mileage that is the same or better with the 302.Up to you man.Its a simple swap once you have all the parts.
my brothers gota straight six and i've got the 302...after driving his i'd NEVER keep a sixer in mine...just my opinion
never seen that good from any of my 6 banger cars. the 'BEST' one that i had was a 200/3sp car that got 26 but most get around 22-24 for me. i've hit 26 on the highway (normally around 24.5) and constantly gets 18+ around town in the '71