I have a W40 (4-107) in my 1977 Bristol 40 Yawl. Which of the Beta engines would you recommend for this full keel boat. I do, by the way, find the Bristol 4-107 slightly underpowered when going to weather in nasty chop (which is when I use the diesel the most.)
I would use the Beta 43 in this classic boat. It delivers much more torque than the 4.107 ever did, especially in the low and medium RPM range. This engine is no larger than the 4.107, has a self bleeding fuel system, is much quieter that the old Perkins and much smoother running.
The whole trick to getting the extra power to the water is to prop the boat correctly. I suggest the largest 3 blade prop that your apeture can accomodate and still allow enough tip clearance to keep prop wash noise down.