Good evening Robert,
In the past I have altered all my Big6’s electrical systems for 12V and possess still a new alternator with 15-6D fan on. As all cars are equipped this way, I would offer the unit for the price I paid 8(!) years ago: 1800€. The unit is ready for use under condition that the other electrical system is adapted. F.ex. the regulator is integrated …I tried to add a picture, but the message field doesn’t seem to accept it. I could send it to your mail address.
Installing alternators into a shell of a 15-6D dynamo could perhaps be done by a company, which Phil Allison recommended to me many years ago. They sold me for 4 cyl. Tractions good quality alternators in the outer shape of dynamos for 4 cyl. cars. Unfortunately I do not have their name and address, but certainly Phil has. If interested in the Big6D unit, pls let me know to send pictures.
Regards
Hans