8 way classics, it was on top.
Dustwashers, like plexi over the CP, didn't show up until the "lets slap this crappy game into a classic cab" era.
All the dedicated classics had the dustwashers below the panel.
Here's a quick list off the top of my head:
1942, 1943, Berzerk, Bosconian, Circus Charlie, Cloak & Dagger, Crazy Climber, Discs of Tron, Gauntlet, Gunsmoke, Gyruss, Jump Bug, Jungle Hunt, Kangaroo, Rampage, Robotron, Scramble, Smash TV, Street Fighter, Super Cobra, Super Zaxxon, Time Pilot, Time Pilot '84, Tron, Up 'n Down, Vanguard, Venture, Xenophobe, Xevious, Xybots and Zaxxon.
Even the Neo-Geo, PlayChoice, and .vs cabinets shipped with them underneath.
I'm sure I missed alot that also had them on the bottom, but I'd like to see a list of classic games that had them on the top.
Some of the ones that I included I don't really consider as classics (notably Street Fighter and the multigame systems I listed).