In the spirit of Fisherboy3's observation that most chinese engine are interchangeable, and to try and help out tjrlang, here is a link to a service manual for a 250cc engine used on a CFMOTO chinese scooter. It is 250cc, has an automatic transmission, and is liquid cooled. I didn't check to see if it had a reverse, but even if it doesn't I'm hoping the differences are only the final output section and are minor. My quad has a 150cc GY6 engine, and the numerous GY6 scooter service manuals have been very helpful to me.
250cc Service Manual Link
Since the link is into a forum specializing in buggies and go carts you can see that this engine is used in more than just scooters. I'm hoping that Masstraxion quads use the same engine.