Tstats are not a precision valve. Look at the shop manual info. Opens @ 167 to 172. Another brand 157 to 162.
You can go up to 180 but 10 miles down the road the wife may fuss that heater is not working.
Attachments
1961 Tstat.jpg (52.27 KB, 211 downloads)

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."