depends on how many horses you want?? I used a 283 with fuelie heads that was overbored .060,with a big cam,carb,intake,mallory unilite,and msd a6 box for years.It worked ok but I still felt that 250-275 horses was weak.I would go ahead and use a 350 if you are not going to stay stock,but most 350 accessories seem to fit the smaller older motors.I had a new engine built from a 350 which has an advantage-it uses modern chevy heads instead of antique tech.Furthermore- a modern crate engine works well,as long as you get modern accessory brackets instead of the antique stuff that I used.