Don't know about numbers; I've got a 73, and they can't even agree on how many were made for the entire year.
As for value, it's almost certainly worth more with the original engine. You didn't spec the engine as original, original year, or not original, but I'm thinking that if it's the original year I'd either keep it in, or at least keep it so you could reinstall it later if you wanted.
As for how much that changes things with it being a 340 v. a big block, I dunno