I have to say that whenever I went to the arcades I hardy ever saw a conversion except for dynamos, but those don't really count. It is crazy some of the conversions you see when you start buying them!
I think the craziest one in that whole group is the Capcom Bowling in the Atari Anti Aircraft II cabinet. It's such a squat little cab, and a vertical monitor looks very out of place in it. Plus, it has a Wico home console trakball on the control panel. Of course several of those Capcom Bowlings have that same "feature".