I believe the cab was a old final fight cab with only 4 buttons per player. As you can tell by my name, I needed 6 buttons for MK3...so the pyramid was the only way to add the buttons and have the layout the same for P1 and P2. I didn't want there to be an advantage/disadvantage for the 2 players. It actually plays quit nice.
The button layout is like this:
2
1 3
6 4 5