Ok just got back.
Good news and bad news. The bad news is that its not a 590A1.
The good news is that it does have a bayonet lug still but not all the A1 heavy duty upgrades that the military demands. (heavy barrel and metal trigger guard)
I also met him at his job and met his supervisor and he showed me his DL and blue card for a handgun so he seems legit.
I still paid $300 just because it was clean and nice looking and I didnt have to pay the $25 BG fee and taxes for a 590 and he threw in a free Flambeua hard plastic case. It would have been a killer deal if it were an A1. It was just an ok deal as it stands and I am happy to own it. I'll ask my dad if he will give me his old bayonet he stole "cough" I mean brought home from the Army back in the 70's just for kicks.
I checked the Mossberg catalog and it is the special purpose 9-shot model as they call it. Gunbroker has them for $379 to $400.