The MK23 is the one thing missing from the USP file here. I do have a KSC USP Compact, a Tanio Koba USP Tactical, and a Tanka USP. I have 2 adapters the really small USP one and the bigger TK adapter and they swap around without too much hassle.
They say the trigger guard is the hitch on the MK23. If it was me I'd either roll the dice with some adapter orders or look around and see who else in the area has one to try out.
If do ever find your self in a spot where you have to break out the files and hammers go at the accessory first before the pistol frame.
Airsoft, where nothing is hurt but feelings.