. . and it didn't fix the problem, right?
Apparently not. I thought it was fixed; the tractor stopped overheating after replacing the temperature sending unit and the thermostat, and flushing the radiator (pulled the plug, let all the fluid run out, ran hose into top & let run for 10 minutes or so, replaced fluid). Immediately after doing this, I was able to use the tractor for several hours non-stop to backfill a trench with the box blade and FEL. No overheating issues at all.
So you still have neither blown out the rad fins nor back-flushed
No, haven't done either of those because until yesterday or the day before, there was no indication that the previous steps I had taken hadn't fixed it. (See above.)
First blow out the fins, (from back to front, common sense), then back-flush
It's fairly condescending for you to say it's common sense. Maybe it's common sense to you; to me, it's Greek. (As a for-example, it never would've occurred to me to blow the radiator out from back-to-front.) I'm not a mechanic, and the reason I keep asking for help is because I feel like we're getting to the limit of what I can comfortably do on my own without causing further damage.
Tractor owner (to Google): Need help with tractor
Google (to tractor owner): See tractor support forum
Tractor owner (to tractor support forum): Need help with tractor
Tractor support forum (to tractor owner): See Google
Ain't the internet grand?
On the plus side, I bumped into a local guy this morning who has a lead on a diesel mechanic that might be able to come give me hand. Not sure what it'll cost, but it'll surely be cheaper than a new tractor.