16 gauge 12s were built on the same frame as the 20. A fine, fast handling and smooth shucking pump.
A couple things......
$200 for a shootable Model 12 in any gauge (they made some in 28 gauge also) is a deal. But....
The big money for Model 12s is NOT for field guns in 65% shape. That's for NIB stuff and for non standard stuff like Black Diamond Trap models.
Not to worry, you'll never lose money buying a 12 for $200.
In your shoes, I'd send this off to either Simmons Guns or Nu Line for a checkover and estimate on a refurb.
Checkover, because all old shotguns need to be checked for safety and function.
Estimate, because these are Forever Guns and fixing one up makes a lot of sense. Your great grandkids will thank you.
And if you ever decide you can't stand to have that in the house any longer, please call me first.