This motor runs so hot that it sounds like it's about to seize,beleive me I know what I'm talking about. My WSC,SD and AC can run for hours with no problems and the crankcase temp never exceeds the limit at which I can't hold it without distress... The AD gets positively piping hot after 20 mins or so I could pipe the water from the block back around so it pours over the crankcase that might work...otherwise I'll just build it back up and run it for short periods of say 15 mins then have a gin n' tonic and start her up again for another 15 mins and so on until my 5 hour voyage comes to an end... At that stage I won't care if the ruddy thing is hot or cold!
Remember,dust and dirt are the enemies of all moving parts...keep your motor clean and it will repay you!
Just before you assemble it, Soak the cyl in a very strong mix of caustic soda and give it a good blast with a pressure washer if you have one. Im sure all AD cyls have removable plugs on the side to clean out all the water galleries im think. Give it a good clean and see whats inside. Remove the top and bottom water in and out fittings and see how you go. When its getting hot, does the tell tale water flow burn your fingers because its steaming so bad.