Those hmc300's were a nightmare and were only made for a few yrs. I don't believe many were sold. The latest 400 series were bullet proof! With many still running daily.
I don't expect there is many people around who could do a 300 series program.
I could probably muddle through, but it's been many, many, many yrs since I stood in front of a 300!
Have you tried contacting united grinding?