I picked up a Monkey Ball GDRom on the shmups forum recently (thanks fuko!). Normally this requires the expensive "banana panel", but given I have a Planet Harriers cab with analog stick, I figured it should be compatible - not to mention a lot less phallic than a banana stick.
Swapping out the Hikaru for a Naomi GD was no problem at all, everything hooked right up perfectly! Booted up the game, calibrated the analog stick, and gave it a spin, only to find the vertical axis (up/down) on the analog stick was reversed. Not sure why Planet Harriers analog controls would be any different than other Sega games, but hacking some disconnects for the vertical pot and swapping the wires around solved it quickly.
Obviously Planet Harriers is a much better game, so I won't be keeping Monkey Ball in there for long, but it does make for a nice change of pace, and I have always wanted to play the original arcade version of Monkey Ball. :) It's also fitting that both games were developed by Sega's AV division.