I think the finish Mr. Ramos is referring to is Beryllium copper-plated trigger mechanism for wear free and self-lubricating advantages on the Combat models back then. Keep in mind that Mr. Ramos book seems to have been written in the late 80's. Another thing I've noticed about the Combat models then, is that on the left hand side of the slide it just said Model 85. No mention whatsoever to it being a special model.
I own another early model 85 Combat made in 1993, but with the ugly LPA adjustable sights. Don't know why they stopped installing factory low profile sights.
On the slide stop subject, I'm going to call tomorrow the importer here in Spain and see if they can help me. I wish we had a Mike over here.