1972 chevy 1/2 ton 307

[Aunt-Jemima]

ok i have a 1972 chevy 1/2 ton 307/auto. its wrecked i need a whole front end clip passenger bed side doors and the frames bent. someone put a floor shift auto in it be the colum was getting stiff and they didnt know how to put it on the fllor so they switched it out for a auto i have no idea what kind it is. im deciding on whether its worth rebuilding or not. if i do i want to know what would be better gas millage a 350 or the 307 but either will be built to around 300 horse. help me decide whether its worth it or not.