Another Motor you might want to look at is a 400 SBC. It is basically a 350 block bored out, the fallback is that you have to have steam holes drilled in the heads, so if you go this way then you should have a VERY VERY good cooling system to keep cool just in case. I would also suggest if you do use it to take it out .030 over to about a 406.
I have one in my garage that I was gonna drop in my '70 Chevelle, because it is .030 over and balanced and blue-printed. If I had gone with some AFR heads, a good size cam, a 750CFM carb or so and some roller rockers and lifters would be good for about 450+ HP and some stunning Torque #'s, and because it is a SBC it is fairly quick to rev, this along with a solid tranny like the famous Muncie M-22 and some good gearing would be an amzing rig.
Just my $.02
