JRM,
If the rifle in question has a 20.75" bbl and is fairly lwt, it sounds like to me it's the M-4100 Lwt. The same rifle was imported by Smith & Wesson as the model "B" or "C" depending or whether or not it had a Monte Carlo stock. If indeed that's what it is, it will have a schnable forend. If so, you have found a rare treasure. If you do buy it and decide to rebarrel, I'd be very interested in the take-off barrel. I have one in .270 Win and one in .30-06. The '06 doesn't much thrill me, and I'd much rather it was a .308...
Edw