As stated earlier, the S means that it was built by Marlin and they started the serial numbers over again, starting at FWS 1. Many of these guns were built by Hunter Arms employees and the price in my opinion does not detract from it being a Marlin era gun.
Most of the ones I have seen have 2 3/4 inch chambers written under the serial number.
At this time all Marlin era guns were built on the Featherweight frame.
If the gun is tight, I think $600 is a fair price. I have seen 12 gauges going for that price. Blue lists 16 gauges as being 60% higher than the same gun in the same condition as a 12 gauge.
