All right well i ordered the steering wheel.

Assuming the worst about the button hole and that a momo-merc three point button won't install, I'm comfortable with having to do some sort of serious electronic workaround to get the connections working. I work with electronics on a daily basis so can figure something out. They weren't able to provide any pics of wheel without the button, nor give a diameter of the hole. But based on pics it sure looks very similar to the momo size, and their own brand of horn buttons for sale seem to be standard for "all wheels". So fingers crossed.

The momo hub adapter seems to be a match on both ends. Fingers crossed on that too though. You never know.