How rare is this car?

For '65 GT's like mine, most were 2 BBL. I expect the same for '67. With a 4 BBL, you probably have the high-compression dome-top pistons - the "Commando" or "Hi-Po" engine. I understand no way to be sure externally, you must either remove the heads or probe thru a spark plug hole (bore-scope or such). If you ever change the cam, keep in mind that the Commando cam had more lift than the standard engine, but still fairly mild by today's standards.