I'm not a DR guy, but maybe the differences are in the EEPROM rather than the MCU, so a ROM transfer may solve the compatibility issue. If the EEPROM is external to the MCU, a ROM transfer should cost you $10 - $20.
However, before purchasing a PCB, I would measure the resistances of each of the motor windings.
Have you tried
http://www.onepcbsolution.com/ ?
If you intend to replace the whole drive, you may need to determine if there is a software zone in the user area. Some DVRs load their runtime code from the HD.
FYI, I have found the following support site to be one of the best:
http://www.videohelp.com/