johnson 140 saga continues

[thebottomfish]

Okay guys, compression numbers as follows 120, 118, 113, 118...So to say I'm amazed the numbers match my compression from last week is an understatement.
Now it brings me to a dilemma...do I pull the heads and try to get this gunk out? Unless I put the head gasket on wrong I assume I can't screw up the compression. Just seems like I should let it be, after all I'm not sure this gunk is there from my recent overheat or of it's been there since I've owned it.
Dilemma two, of course I want to put in thermostats but since they weren't in there from the previous owner I'm not sure I should, for testing purposes right now...thoughts?
Warning horn didn't work when the tan wire was grounded and I ran hot lead direct to the warning horn so I think it's the horn that's toast...guess I gotta source one of those.
And I get to try my hand at replacing the water pump which I knew from the get go. Any tips disconnecting it from the linkage?