We have to ask what pulley sizes you are using on the ND vs. the GM alternator. If the ND holds up better than the Delco but has a bigger pulley and turns slower it is an unfair comparison. You can rebuild a Delco 12SI for a lot less than a ND as well, in fact some of the NDs are throwaway and are not rebuilt.
I always get frustrated when people say they have a Toyota, Honda, BMW, Jaguar, etc, etc alternator. None of the European or Japanese car makers make their own electricals. They are a Lucas, Bosch, Marelli, Paris Rhone, or a Nippon Denso or Hitachi, or what have you. They may be used on a Toyota, Nissan or Honda or a BMW, Peugeot, Rover, etc. but often these makes use different vendors. It helps to know who made the unit itself and what an OEM application was, but even one model of car had several vendors and models of part.
GM always used Delco (almost always), Ford had Autolite/Prestolite and Chrysler built their own usually. This is unusual in terms of the worldwide market. I think Chrysler and Ford both had some Leece Nevilles for heavy duty applications.
