I purchased one from SFRC during this falls DUCKS sale, I see they have 3 left. It was oily with some sandy grit and a couple insects to clean out. It is a factory 6635 with a 24 million serial number, so circa 1980. I has a short collar threaded barrel, stamped trigger guard, late rear sight block with the rear leaf marked "3" and a 2 piece gas tube.
The stock has been sanded but it still shows battle scars. It has been refurbed as the blueing is very good with some slight pitting on the receiver and gas piston. Nothing matches, except the rear cover which shows evidence of grinding and stamped to match the receiver.
The good news is everything is tight, crown and bore are very good and has a decent trigger. Not bad for $200 and change.