Turned out all I needed... and the previous owner, who cooked the head,
as well, was a $10 thermostat. Shows you what a little strategic
neglect can do.

What I pulled out was some aftermarket mess, and even if it opens it
doesn't have the throughput that the original supplies.

Drove it all over the place this evening, needle always shy of the LED,
the way I like to see 'em.

By the way, I replaced the thermostat in about  15 minutes and didn't
have to bleed the system. I took six pieces of wood approx. 3/4 x 1,
two for each hose attached to the water pump, and three c-clamps.
You'll never get the clamps down into the cramped quarters around the
pump, so you need clamp extenders in the form of the sticks. I held one
on each side of each hose respectively with one hand, like I was trying
to pick up the hose with giant chopsticks. Then, up where I could reach
easily, I put a c-clamp to squeeze the sticks together to clamp the
hoses closed so that very little coolant leaked out. the thickness of
the wood transfers enough mechanical advantage to squeeze the hoses
shut.

Then the thing ran SO BADLY that I thought I had done something
terrible to it... turned out to be an old split fuel line, readily
replaced.

I thank everyone on this list who helped me, and who must have been
wondering "why doesn't he take this to the diesel list?" I've been to
every diesel list on the Internet, and believe me, this list is where
the help is! rock on.

Jim