Microsquirt, but yep. It seems like some folks have sorted this out, I've found a few installs out there on some RZ/RD Yamahas, and some people asking questions about installs on snow machines and PWCs, so, it's out there, but tough to say. At this point, I don't have much to lose!
Your site, Konrad, will be invaluable for piecing the whole thing together, to have the values for the sensors already is a huge leg up!
There should be plenty of room, the Microsquirt is fairly small, and watertight, so there will be room under the seat for sure.