If you throw a big block in there, you're going to have massive increases in torque, which would be great for the drag strip, if you could get it to hook up, but not much good on the street. Yeah, it'd be cool. I have a BBC sitting in my garage right now, but it's not going in my Z. Too much weight, too much torque, and the grin per dollar would go down a whole lot. Example, my dad has a 69 el Camino with a BBC that's bored a bit, cams, good iron heads, and NOS. It pumps between 350 and 400 HP as a mild build, off the bottle. My 383 when it's done will be around 450-500 HP. 650 if I can talk the guy I work with into letting me put his V-trim supercharger on it. I'll have about the same amount of money into the small block as my dad has into the big block with more power and less weight. IMHO, if you want to be different, throw the big block in there, heck, throw a 928 motor in there, God knows I've thought about it, but if you want reliable good ol' fashioned fun, stick with the small block.