Hi 4V,
Thanks for the reply.
I've got shutoff valves installed on my heater hoses, so during the summer no 'bypassing' is happening thru the heater core....
Update: I pulled out the solid restrictor plate and installed one of Tim Meyer's solid brass bypass plates in its place:
https://www.tmeyerinc.com/prod...estrictor-cleveland/
The 333-195 and 333-180 thermostats are readily available again (for now), so I decided to revert back to the original scheme. To round out the cooling system updates, I will be installing the FlowKooler #1648 water pump, and possibly updating to George P's self-bleeding header tank modification.