I only know they were produced during Mainship's hiatus from the trawler world, which lasted roughly circa 1990-1998 or so (give or take, plus or minus). The first Mainship boats were produced by Silverton (Mainship wasn't a separate brand then), in Marlboro NJ. The story as I understand it is they acquired some 34' downeast/lobstah-boat-like hulls, finished them as sorta-kinda trawlers with single diesels, found them popular, so they made and sold a boatload. Augmented by similar twin cabin (aft cabin) models, 36' and 40' I think, usually with twin gas engines.
Then eventually Mainship became it's own company, a separate subsidiary of Luhrs Group. That did not happen prior to 1987 -- our '87 34' MK III was built by Silverton in Marlboro -- but I don't know when the transition took place. Mainships built in the '90s were mostly twin-gas sedans and motor yachts of varying styles. (A dock neighbor has twin diesels in a 40' but he did that conversion himself and I think it started life as a gasser.) One of the brand's useful features was the incorporation of easier bow access using a centerline "staircase" (walkway) from the flying bridge. (Silverton, in the meantime, adopted a "sidewalk" approach, which was equally popular. Both brands eventually began using stairways -- not ladders -- to the bridge.)
Then I think around 1998 or 1999 or so (+/-) Mainship began introducing trawler-like boats again, with the 350 (later 390) that essentially upgraded all the things "missing" on the original 34s (stairs to the bridge, wider beam, centerline master berth, sliding doors from lower helm to the sidedecks, etc.) More trawler-like boats (430, 400, 30 and 34 Pilot, 34T, etc.) from then on.
Then Luhrs bankruptcy, Marlow acquired Hunter and Mainship, Egg Harbor Group acquired Silverton, somebody else acquired Luhrs...
The '97 MY you've seen would have been one of the non-trawlers. Likely decent quality for price, probably gas engines, likely with a couple progressive deck features compared to other brands of the same era, decent systems (ACs, water pumps, heads, etc.), but then everything will depend on how it's been maintained and so forth.
There's a Mainship group out there somewhere; I think on yahoo...
-Chris