I too have a Captain America cab that was converted. Mine was converted into a neogeo. I personally would never do any damage to the cabinet I'm building in. I don't believe in doing any permanent re-wiring inside the cab, adding extra buttons to a dedicated (not converted) game, adding kb trays, or any type of insane rotatable monitor setup. <GRIPE>I might get flamed for this, but IMHO, I -hate- seeing more that one control setup on one layout. For example, I've seen cabs that have 2 8 ways with 6 buttons each, 1 4 way with 2 buttons, a trackball with 2 buttons, and a spinner. If you have enough skill to do a MAME conversion, then you have enough skill to buy some molex connectors and a saw and make swappable layouts. </GRIPE>
Using a j-pac, a powered computer subwoofer (NOT the speakers), a new Happs power supply (so I can plug in the sub and computer on the inside), some molex connectors, and quick disconnects I've managed to -convert- my cabinet to a MAME cab, not actually MAME my cab. I can take out the PC and replace it with a JAMMA board in about 5 - 10 minutes and no one would ever have any idea a pc had been there. So in other words, feel free to buy a classic game and convert it (as long as it's JAMMA, though jamma and classic are kinda mutually exclusive) as long as you don't plan on drilling holes or super gluing cupholders on the side.