I got a refund from Dack and ordered one from G&R, which arrived yesterday. I was just messing with it and my new MR920. I will have to turn down the cover plate screw heads to make them fit but otherwise the mounting plate fits tightly with the thickest spacer Shadow Systems provides. It does sit significantly higher than the RMR and 507c/508t, so the stock irons aren't going to work.