I have done Ridlyme twice on my 1981 5411. Disconnecting the intake and return and running the engine with the hoses in a bucket till a half gallon was gone. I let it sit overnight then restarted with a 5 gallon bucket of fresh water till cleared.
This has proven very effective and now the engine runs at 160-180 continuously, this is at approximately 5 knots for no more than 2 hours max. Tom C27 My Tern
