Try loading the 640K PUFF_253 full bin/boot followed by the PUFF_295. You will lose all your setup etc, so save it and restore via user setup, and installation rescan, or save it under Chanel Master and restore that way.
If you are not successful then you should do a "revert to 2500" using special loader by Chancy and b60 boot, then old 294T file and then the full conversion