Karl says:

"The only part I haven't found is a small coolant pump that
could be run constantly at 200 or so degree temps. "

For the small radiator, a heater core would do nicely.  I've seen circulation pumps (electric) listed in laboratory apparatus catalogs in all shapes and sizes years ago when I dabbled in chemistry as a hobby.  They are made to withstand harsh environments.  Getting a 12V. one would be difficult.  Perhaps a 120V A/C inverter setup?

--Nate