An interesting question. We have been repairing mechanical and electronic speedometers for 15 years and have tried to follow this question.
I think the dealer should be able to program the digital clusters from 96 on see:
As to 124 body digital, I really don't think MB has a plan for it. See: http://www.dashmaster.com/frames.htm
for a more simplistic prom burning approach.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
[This message has been edited by stevebfl (edited 03-18-2000).]