Most of the alternators on eBay are the single wire jobs with a built in (dumb) charge controller. If you're using anything more sophisticated (even like my old AutoMac) you're going to have to remove the internal controller and get the field lead external. You can do this yourself or have a local shop do it for you. If you have a decent local shop, you might be best off telling them your needs and seeing what they can do for you.
Even though you have a diesel, I'd recommend getting an alternator with the marine anti-explosion screens. They will be identified with an SAE number, but I don't remember what it is - perhaps 1726? Google it.