Thanks Macbeth!!
I originally remembered an A19 version, but the Google Cache of TiN's page only shows A15, so I figured I was hallucinating. The checksum is just a simple 16-bit checksum, so I guess can be easily re-created if necessary. I have correct dumps of A05 if his are wrong, and will upload when the site comes back online.
I purchased flash to replace the EPROMs so can play with versions at my leisure. Trying to solve problems with the RS-232 interface flaking out.
Thanks for the tip on dumping the cal EEPROM. I don't have the proper clip leads to do this but will bodge something together.