Ive given some thought to what really goes on in the 560SL's EZL (later cars may be more sophisticated) and there is probably a microprocessor with a map of vacuum (load), wide-open throttle (digital switch), coolant temp and RPM built into its ROM vs "proper" advance of the ignition, in front of the big transistor switch that fires the coil. The reference resistor changes the map.
It would probably be easier to build an entire new module from scratch, the problem with that is certifications, etc. The connectors are unique and would require some tooling. There are some clues in the shop manual on what the map might look like at a few points but who knows what it is outside of those points. Heh, heh, you could probably reverse engineer this by developing a "spy" piece of hardware with software that would record all of these parameters vs the ignition advance, and drive around with it for a while!
It's a damn shame that it's sealed and potted because 99 out of 100 times, it's probably the big transistor switch.
If Programa actually wanted to do this, I'm game to build and program it
