Judging by the pictures, you'll need some major modifications (primarily just adding a second gun) to get anything newer than Call of the Wild. But once you have that second gun, you could upgrade all the way to World with a computer swap and possibly (probably?) a little rewiring.
I strongly recommend talking to Betson (who actually makes all the BBH cabinets) directly; it's very possible they make a conversion kit to upgrade BBH1/2 cabinets to the Pro-and-later style.