That's a Mark 1, made circa 1980. I'm sure someone else can pin down the production date. I have D8xxx, that should be very similar to your gun. Mine has the frame serial number hand-scribed on the disconnector rail of the slide, and also on the bottom of the barrel. $450 is a good price. I would recommend installing fresh recoil and magazine springs. There is some good historical data available at this website. I assembled a collection of contemporary Detonics quotes and press releases from various gunrags, and you can find that at sightm1911.com.