Would a 27C040 in the plcc32 package (like a 27C040-70JU) work? I can't remember what I used to reflash firmware in my scopes, it was a while ago..
If you have a reflashable chip, why not copy out the firmware, verify it a few times then flash in the later firmware?
I have put a few versions up on tekwiki. Just flash the latest to the newest until you find one that works. (TDS210 and TDS220 firmware is the same)
https://w140.com/tekwiki/wiki/TDS220As for the TDS210/TDS220 thing, all of these scopes are capable of TDS-220 performance. What differs is the sticker on the front and how it was programmed and calibrated.
It is possible to upgrade a scope by sending the following GPIB commands:
PASSWORD PITBULL
MODEL TDS220
Followed by a full calibration to turn a TDS210 into a TDS220 and make the change stick.
(You can also downgrade if you wanted for some reason too)
If cal fails, the scope will revert to its previous model, so the entire proces will need to be repeated.
I'm not surprised that a preproduction unit would be configured as a TDS220 to allow for more complete testing.
Also, do you mind taking some nice photos of the unit inside and out? Including the main PCB?
I'm interested in seeing how it is different...