The "solenoid" of the E start quit, forcing me to kick start Timex. Doing so has rehabilitated my formerly dodgy knee.
That said I do keep the E/S just in case.
Retro fitting the E/S to a K/S only machine should be do able with some parts swapping a little plumbing and a bracket fabrication.
If a body gets lucky and finds a complete E/S system that had never given any trouble ( knock on wood ) then I think they would do well with it if it were properly used and maintained.