Well, I remeasured the control panel last night, and it was 4" and not the 3" I thought I remembered. I tested the setup with a junked joystick I had, and it looks like it will handle a standard joystick just fine.
This is going into a small Pitboss bartop cabinet, and it didn't look like it would handle a full-size joystick. Since it will, I'm going to be putting a Happ Super on it, 3 game buttons, a Ms. Pac/Galaga 4-way joystick, and P1 & P2 start buttons.