Update -

Water Pump is a German one from Van cafe. It feels OK, so I'll think I'll
leave it be. The t'stat housing came out OK with the water pump in place.
I recall heeding this list's advice 4 1/2 years ago and using anti sieze.
It worked. The heads of two bolts holding the flange did snap off, but I
was lucky in that there was enough stub remaining to get the rest out with
vice grips. All threads cleaned up easily with a tap. All contact surfaces
also cleanded up nicely.