Frankly, I am at a loss as to why a person would change an engine in the first place. We have the Perkins TMD 22A Turbo and it runs like a gem. I can still reach the hull speed of over 8 knots and I can still power into a 30 knot + head wind and still make way comfortably. The engine has proved to be very reliable and economical to run. If you put two identical Amel's side by side, one with a Perkins/Volva 80hp and one with a Yamnah 110hp and ran them flat out, I doubt if you would see any difference except a larger hole in your pocket.
It is my opinion one would be better of spending the money and giving your existing engine a full overhaul. The Perkins is a very good engine and if the maintenance is kept up, like any engine, it will provide many hours of service. I know I can get parts anywhere in the world so why bother?
Just my two bob's worth.
Barry & Robyn
Tradewinds III SM #171