Finally, overheating is my bitch!

I admit that this problem went on way too long.  I'll also admit to missing a vital step in troubleshooting and not seeing what was right in front of me.  The important thing is that I only spent $1,000 and not $12,000+!
To recap, this engine has overheated repeatedly ever since we bought the boat.  Usually at the most inopportune time possible.  It is really nerve-wracking to hear the overheat alarm squealing as you transit the mile-long, very narrow, channel into Boca Chica.  They blasted and dug the channel out of solid coral limestone to enable fuel and ammo barges  to get to the Naval Air Station back in the 1960's.  The tidal currents are rapid and there is barely room to pass two large yachts.  Lose the engine and you may lose the boat!
Micky has not been feeling well, so I have been trying to troubleshoot alone.  The result is that I could not be both on deck running the controls while carefully watching the engine below decks.  My shortcut was to just flip up the top engine cover and check temperatures with the IR thermometer.  I put a new impeller in the raw water pump soon after getting "Tango" and did not start my troubleshooting there.
That was a major mistake.  Even though the mixing elbow was original to the boat and was indeed clogged and corroded, it was not the major problem. Today with Micky doing the button and lever thing on deck, I was below and saw the problem. The raw water pump was not rotating.  It was seized solid on its shaft.  The drive belt was nearly worn through from trying to turn the stationary pump pulley.
Mark DeJong is one of those free-spirited, hard-working, indispensable men that seem to gravitate to the Keys.  His schedule is loose, but his logic is tight.  He has an open-air, semi-shipping container, Butler building maybe sort of a shop at Robbie's haulout yard on Stock Island.  His girlfriend, Meghan runs the place and keeps Mark on point.  Stuffed somewhere in there among the artistically painted paddles and rusting cannon are parts for just about anything that Yanmar or Kubota ever made.  I need to take a picture of the "Muffler Man"  Mark built.  Welded together out of crankshafts and ring gears, leering insanely is a life-size Gatling-gun hip shooter complete with a draped belt of 7.62mm linked ammo.
The pump Mark had was not technically the right one by part number, but it would do the trick.
Now the engine bangs happily away at 160 degrees and is much quieter.  I also spent 40 minutes freeing up the rusted stuck idle adjustment and restored the unit to 850 RPM idle.
All in all a very happy day.  Monday the rigger will come and help fix the furling jib by installing a halyard restrainer at the masthead.  We will also install a strap at the bottom to stabilize the drum and stop the whole thing from riding up the headstay.