Thank you all for the thoughts!

I believe the new water pump pumps in the same direction, but it might be "high output." The JEGS catalog was not clear on that.

Is there such a thing as a "high output" thermostat? Or, how big of a hole do I drill in the flange?

Should I just run it without the thermostat for a while to see what it does?

Is there such a thing as a "high output" (i.e. stronger) hose?