Disklavier

I am looking to buy a used Yamaha C3 piano with DiskLavier.  It was
built back in 1991.  I am struggling to find the diferent electronic
components and their respective models over the years.  How do I know
what features it has? How upgradeable is it?  Is it even worth
anything over and above the value of the instrument alone.  Could I
"Slap" a Mark III unti in its place, and be automatically "up to date."

Can anyone help?  A reference of all of the different models and
accompanying details would be great!  Any such luck?  jb