I found this boat advertised as a 1978 Marquis 31'
Anybody ever heard of it? Any good or run away as fast as possible

I had the very first one built under the Lancer name back in 1976, Jim Klem,, [Klem Gem] sold them.. Many west coast builders made them under many names like CAN AM in the later 70's.. They have a wet ride @ below 40mph

So is this hull a copy of something? Or a stretched something?

The company started out coping a 30' Scarab, & that did not go over so good. Lancer of California then made there own plug [ not a copy of any hull ] after I put the money up with Klem to make it happen. The hull design was just OK but it was built well. These hulls had a wet ride with small block Chevy's engines. I later put in all cast iron 454 Mercruiser engines & it rode better with the extra weight in the transom, but it never rode as good as my Magnums do.