From what I remember, (My Winchester book has been misplaced) The model 670s were a more basic model (Sportman) of the Model 70 push-feed action introduced around 1966-67 and made until the mid-late 1970s. They made a 19 inch carbine, a 22 inch sporting rifle and I think they even made some in magnum chamberings with a 24 inch barrel.
They had a stock made from less expensive wood, and I believe they had a blind magazine. The checkering was pressed and not cut. Also the bluing was more of a mat finish and not a high-grade blue.
From what I remember I saw one that did not have the famous M-70 three position bolt shroud safety which locks the firing pin in place. instead they had a cheap sliding trigger blocking safety like a M-700 Remington... But not as nice. Maybe that was some sort of weird deal that somebody did to that particular rifle...
Because I have seen photos of others that did have the 3 position safety.... WEIRD...maybe there was another sub-variant..
EDIT:
I just took a break and looked up the few that are for sale, I am getting old and sometimes mix up rifles i have seen.,,, all had the 3 position M-70 style safety, EXCEPT one,,,, which showed a close up of a different bolt shroud and safety.... Wow...
I remember seeing them for sale in places like K-mart, Western auto and so -on during the late 60s -early 70s. But only a couple. I do not think I have seen one in person for over 30 years.
The M-670 are about a $300-$399 rifle and they may not be easy to sell.
On the plus side, you could probably buy a push feed M-70 stock and floor plate assembly and basically have a low grade model 70.
What are you talking about when you say bolt assist on the Mauser???? Did the bolt throw itself rearward when you opened it and it had not been fired??? If so it was a model of Mauser prior to the M-98 Mauser. Such as a M-93, M-95, Swede M-96. They are a small ring Mauser and are not as string as a large ring M-98 action.