How much money are you looking to spend? What kind of power are you looking to get? How is your suspension setup?
I would personally go with a 489-510ci BBC. All the power still may not get you to reach your goals unless you have the suspension to back it up. I will be building a 505 or 510ci here in the next month putting out about 600-650HP for my 1971 Chevelle....cant wait!