I dunno where FR is doing it nowadays... i did see some pics and a write up on it... anyway, there have been better floyd rose designs out there, and I think FR has a long way to catch up.
With davis, they basically have 2 types of FR screw in arms, the ESP and Schaller. The Schaller is the one that would fit.
It would matter if its metric because the whole arm assembly is purchased, not the arm alone. So you can take out the old arm assembly and install the new one.
unless jap arm assemblies can't fit into an american OFR's arm holder hole?