Devin;

Double check it by submerging sender in a cup of boiling water...that'll tell you if its working pretty quick!

Some years ago, I adapted the sender of an electrical guage into the hole in the head...I seem to recall the adapters (SAE sizes) that were included with the guage had one which fit...but it just wasn't the right thing...

A working temp guage is might important to monitor the (new) engine...and to make sure the thermostat opens...it would be a shame (and expensive one at that) to cook a fresh rebuild.

Cheers