OldCrankman
Scott,
You are correct that the RE-199T is at least a 1971 model; it replaced the former RE-189T Lawn Champ sold for 1969 and 1970.
I think your mower sounded pretty good for being 53 years old!
Here's a video of my 1983 Sears Craftsman 914126 (same as the Sunbeam 4318):
~Ben