I ended up with a used Manners EH1FA that had one of those Henderson RSR's already inlet in it, have used it to attach a few different ARCA rails. It's ok. The EH1FA forend has a slight curve front to back (in addition to side to side, of course) so the RSR isn't flush and the ARCA rails are very not flush. After a few matches with a heavy 360 Precision rail on it, all the screws loosened out and I had to pull the action to correct, because the screws go in from above as opposed to the normal T-Nut attachment in stocks like this. Since that correction, it's been fine for another match and a few practice sessions.
For me, going forward, I'll stick with drilling holes and installing T-Nuts so that I can change out/service an ARCA rail without pulling the barreled action. If the RSR loosens up again, it's getting epoxied in place.