What years was the Model 120 Magnum made and does anyone make rifled barrels to fit this action?

I have just purchased a Model 120 myself, and have been looking to gather some information. So far I have found that the Marlin Model 120 was released to sale in 1972 for a whopping $150. I found this information from an ad from an old magazine that was for sale on e-bay.

The Model 120 shotgun, manufactured in 12 ga. only, was introduced in 1972 with limited production; full production followed in 1973. It was cataloged through 1985 (not sure about '86 and '87) but did not appear in the 1988 catalog. There were a variety of barrels made by Marlin for this gun including 26" IC, 28" M and 30" F with rib, as well as 28", 30" and 40" (later shortened to 38") plain barrels. A 26" slug barrel with rifle-type sights was offered in 1973, and later was shortened to 20". These were not rifled tubes, but rather bored to handle slugs and buckshot. They included a provision for scope installation as well. I have owned one of these guns since its introduction in 1972. In the mid-late 1980's I began a concerted effort to find a slug barrel for it. None of the aftermarket barrel makers have ever offered one (at least that I am aware of). I was lucky enough to find a modified plain barrel that somebody had shortened to 20" and installed front and rear sights onto at a gun show about 20 years ago. I have never seen a slug gun for sale and occasionally see a 26"-30" gun advertised on one of the Internet gun sites at prices ranging from $200 - $275. I believe that the gun was underrated as it is every bit as well made as its competitors.