I want to check out the thermostat in the '59 292 in my Model A.  I have read that chemical cooling system flushes are not great for older engines.  I have watched videos where they use a garden hose to spray out the engine (with thermostat removed).  I REALLY hate antifreeze and don't want to put my dog- or anyone's- at any kind of risk.  

It isn't running hot- quite the opposite- so I have no reason to believe anything is gunked up.  

Am I just overthinking this?  Should I just drain it, check out/replace the thermostat, and refill it with new 50/50 antifreeze and distilled water?

I have restricted the flow at the bypass hose or bypass hole on other engines but never saw the need to do so on the Ford Y.  Most heating problems on my end center around the lack of air flow through the radiator and/or inadequate water flow at low rpm.  Once those two issues are taken care of, heating issues are typically taken care of thus not requiring to go so far as to put a restriction in the bypass hose. 

I don’t own a Thunderbird though and if I did, I might consider it if I had a heating issue.  With some of the recent advances in the one inch spacer plate technology for the Thunderbird engines, the need for a restriction at the bypass hose may or may not still be needed.  On the flip side of all this, the SBC circle track engines tend to like that bypass hole in the block behind the water pump restricted or blocked to aid in cooling.  As long as the thermostat is open, I don’t see a problem with cavitation issues.

Lorena, Texas (South of Waco)