Earlier Asteroids cabs (and I'd say most of them) have the G05-801 monitors with the 3 separate boards. Later ones have the G05-802, with two boards. Just google schematics for each, as separate docs exist just for the monitors.
There are 6 or 7 different revisions of the game board, though they are all functionally the same, in terms of how they plug into the cab. If you have the latest (7th) revision of the Asteroids schematics, it explains most of the differences. But that's really only an issue if you're doing board-level repair.
Note also that the two monitors technically should use different power bricks (as they use slightly different voltages), so you may notice that the pinouts for where the harnesses plug into the bricks are different. However many ops hacked and modded these, so your cabs may or may not be 100% original.
If you have any other specific questions, post them here.