big block or small block

[trucker677]

Hi guys, I am new to the forum and am looking at 1970-72 chevelle to rebuild/restore. I am wondering what are you guys are running for powerplants, big blocks or small blocks, I have rebuilt several cars but have always ran small blocks but I am going to keep this car for a long time so I really only want to do this all once.
If I decide to run a 454 will there be a huge difference in fuel mileage between that and a 350. I never had a big block before but I see a lot of chevelles have it. I just want the car for friday night car shows and driving on sunny days, it will be laid up during rainny days and winter.