Steve, go bigger than the 4-108., Knowing you and Brendon I'd try to find something bigger than a 50. I have no idea what's available but think even something bigger will be lighter and smaller than the old 4-108 as well probably using less fuel as a bonus.

Just read about the Beta Marine 60 and saw a few posts from owners. They seem to like them as you can run them around 1,800 rpm instead of that noise rattling 27. Stingy on fuel also. You motorsail a lot. A big engine lugging along at 1,800 for 24 hours or more could be a dream and you'd have a happy engine. When you need the power it's available.