Curiousity has the better of me too... I was wondering if the slide cut for the adjustable sights with the protective ears on some of the earlier 39xx/59xx guns is big enough to mount a RMR base to... I know that whole sight assembly is removable, my 5906 actually has a Millett adjustable sight on it instead, but I just don't recall what the mounting method is...
I have an extra 39 slide I want milled down even with the sight cut and drilled and tapped for an adapter plate. The plate would hold down the plunger that the sight currently does. I had one firm reply that they could do it, but lost the email before I cold try it.