Currently it looks like its time for a repower (cracked head, pitted cyclinder liner on my Yanmar). This is to go into a 1979 columbia 10.7m (35 ft). She displaces, 18,000 lbs pushed by currently a 14x14 3 bladed prop. What engine would you recomend for ease of swap and proper power?
I would use the Beta 25 or Beta 28 on this boat. Both of these engines are smooth running fresh water cooled diesels that have more power than your old Yanmar used to have when it was new. Both are lighter and much quieter than you are used to and they can both be supplied on the correct mounts to save you having to modify your engine beds.
The Beta 25 should give you about 6.9Knots with a 14"x9" three blade RH propeller. The 28 calls for a 14"x10" three blade.
I would use the 25 if the boat were mine. However if you want to use a large alternator (100 amp), I would go with the 28 as it is easier (and therefore cheaper) to fit a large alternator to 28 which is physically a larger engine than the 25.