my 390 is a single. When i first started looking at 390's I wanted a twin but none were available. Most 390's were built as singles with a bow thruster. I ran a twin engine boat for 25 years and had no trouble with the transition to a single. All 390's are shaft drive. I don't believe that Mainship ever made a stern drive boat, although thay did make express cruisers for a while and I guess it is possible they made some of those with astern drive.
You can go on Mainships website. They have a section titled "previous models" that will give you details on all models past and present. Mainship closed down operations earlier this year and are in the process of reopening sometime in the near future as a division of Marlowe Marine