Claus:  "the best engine" is a tough question to answer.. here is a link for members to a slide show of images of engine compartments in Westsails. 

The best engine is something you can afford, about 35HP, has a heat exchanger and the right transmission and prop diameter/pitch, will fit in the space etc.

Pygmalion W32 had a volvo MD2B 25hp salt water cooled and after ~30 years I was able to install a new Beta 1505 38hp with Bud's assistance.  The difference is like night and day in performance, power and reliability. The Beta is lighter and much quieter.

Hope this helps and good luck.

Jay