I think 3 wheels is possible in Mame, although a 2 wheel cabinet may be more practical in terms of space needed, games supported, and monitor size needed. I have a couple of dual wheel games in my living room right now, Badlands and Sprint 2.
Not to mention the fact that it would be MUCH easier to find a donor cab with only 2 wheels. Sprint 2 is a good choice if you can find a gutted one, or ANY dual wheel conversion game.