Went to a nearby gunshop this morning to check out a gun on their web site. Turned out to be a very nice Mark IV, Series 80, Gold Cup National Match, produced in 1986. The previous owner had installed a FLGR, which I've replaced with a standard GR and spring cap. It has a replacement extended slide stop, and I believe the grip screws are replacements for original slotted head. There are no marks on the breach face, and the only marks seem to be an "idiot" scratch behind the trigger.