What's your goals for the car? And keep in mind that they might change a couple years down the road. Maybe consider a platform that you can easily modify in the future if you're looking for more power. How are your mechanic/fabrication skills? You might need to make a few custom brackets and mods w/ the big block.
As far as motor costs, I don't know that its a big difference. I found a '71 Newport w/ a 440, 727 and 8 3/4 rearend. I paid $600 for the whole car and scraped what was left after I stripped it for $200 (that's motor, trans, rearend and various other parts for $400). When it comes to rebuilding a motor is the cost any different if its a big block or small block? All of the machine work is the same right?
I will agree that the parts needed to fit the big block will drive the cost up.
The benefits of a small block would be lighter (w/o adding a lot of aluminium parts to the big block), more room for things like exhaust, power steering, brakes, AC, etc.
Personally, I like the look of a big block stuffed in an abody w/ the motor almost touching both of the fenders and the hood! It drives just fine w/ manual brakes and steering too. I have a '74 Scamp as well. Scamps don't really turn a lot of heads but when it's putting out 550 hp it sure will!
You'll have fun w/ it whichever direction you go.
