Originally Posted by WilD
I'd lean toward speculating it was produced by Bob Long's shop.
I'm with WilD. There are enough similarities to other Bob Long cockers (ano, pneumatics, HPR) to suggest it's a custom gun that came out of Bob's shop during that time.
Is the back block threaded on the back side for a screw in tourney lock that fits over the cocking rod? That's a pretty standard feature on later Bob Long guns. Here's an example: