One thing missing from this thread is the fact that higher-output alternators tend to require a higher engine RPM to start charging. This is less-true of the newer-generation Bosch alternators that are covered with fins & vent holes. I believe the one I used for my 617a was from a Saab or Volvo... but various MB sedans had them also. At idle my "ALT" light would come on. I eventually kicked the idle up slightly and somewhat solved this problem - the light went off but charging was weak until driving.
Do NOT get one of these "modified" alternators that were rigged for higher output. The numbers sound great, but they are destined for failure because the internal components are running to their maximum limit.