Robby,
Congratulations on your purchase. To answer your question, no, your 27 is not a one-off. Although I don't know exact production figures, there were other 27 walkaround inboards built in the 70's. As a matter of fact, there was one for sale in Long Island NY about a year ago. Unless someone has a phone number they can PM you, I believe the best way to contact Bill Potter is through Don Herman at HermCo,
www.hermco.net .