After a little confusion about which starter I needed to purchase I realized I had uncovered a bit of a mystery when it comes to the W50 engine. According to Westerbeke they only built that engine till 1979. (Model history attached). I suspect they DID build W50 for a few more years when Tartan switched engines later in the 1980s. The two W50 models have a distinct feature difference.... the position of the starter. The first version of the W50 has the starter mounted in the middle of the engine pointing towards the transmission... this has a two holed starter flange. The later W50 model has the starter mounted on the backside of the bell housing pointing towards the front of the engine. This starter has a 3 holed flange mounting.
I have included the spec sheet for the W50 and W52 to show the difference in starter mountings. The newer W50 model adopted the W52 starter location design. I don't know of any other difference in W50 models except for the bell housing, starter, and starter location.
Today, 2/11/19, I confirmed with Westerbeke there were two different W50 models. The older model with the starter located center was discontinued in 1979. The 2nd W50 model incorporated a new common bell housing and starter located aft of that housing. They began this production in 8/1979. Mystery solved....
AND THEN THERE IS THIS "Universal Engine" mystery that I won't get into.
http://www.tartan37.com/t37forum/viewtopic.php?f=3&t=1086&hilit=bought+engines&This does not list the newer W50 model that started production in 8/1979
Westerbeke model history: https://www.westerbeke.com/pdfs/model_history.pdf W50 specs with picture:https://www.westerbeke.com/advanced%20specs/w50_2.pdfW52 specs with picture:https://www.westerbeke.com/advanced%20specs/w52.pdf