What do you mean by an over rated 318? I'm just curious since I don't know much about motors or why a 73 would be that much different than an earlier model. I'm assuming they could all be rebuilt similarly?
About what 74Dusted said. While I don't have the numbers right here I'd bet the 72-73 340 developed around the same horsepower as the 70 318. That's why I said it would be best to build them to 70 340 specs. If someone is going to do that it would be best to start with a cheaper base like a 360 or a 318. The money spent for the 340 could be best spent on the guts of a 360 and you'd be netting a lot better Horsepower to Dollar ratio.