I had an MD5B on my 1983 1800 Alcedonia which served us well for the nearly thirty years we sailed her. But friends Peter Pitchforth and Charles Marchant (both now sadly deceased) with their 2800 Positive Thinking changed to the Beta which is advertised in Dufour News and were very pleased with it and found the company very helpful. Other members may know more details about size etc.
Good luck – Anne Rickwood