There is a "B" in front of that serial number. That would explain why my dissassembly guide was a bit out of whack. I took everything apart and did the polishing route and trued the release points on the sear and striker,as they were not square to each other. Better, cleaner release and a bit lighter (not quite a pound). Not bad.
Then I remembered I had some 'Sentry' specialty lube from my M14/305 playdays. I gave all the mating & pivot surfaces /points a treatment, cured it as per instructions, and what a difference that made. Basically a variation of Moly, it made a very nice improvement on the pull, smoothed it out even more and lightened it another pound plus. Trigger is now at around 4-4.5 lbs, fairly crisp for what it is, but much smoother overall. Nicer indeed. Too bad there's no way to safely trim a 1/8 or so off of that sear / striker engagement. She's still a long pull, but at least it's liveable now.