None of my books cover the commercial chassis for 1959, but knowing what I know about Delco alternators, I would guess that it is a Leece Neville, however, it doesn't matter much, because parts for those high output alternators are next to impossible to find, and finding someone that is old enough to remember them is also difficult. I had my 1969 CC alternator rebuilt when it came back from Ed's. Trucking company forgot to turn off the battery switches, and then when they tried to jump start the car, they must have hooked the jumper cables up backward, and blew out a couple of diodes. I had to hunt down parts, and I lucked out when Kevin O'Connell told me about a place in downtown LA that still had parts. I got what I needed to fix my alternator, and when I spoke to Kevin before his passing, I learned that the shop that had all the old parts for both Delco and Leece Neville, had closed their doors.
The best that he can do is to install a modern alternator on the car, along with new brackets etc. It is going to require someone with fabrication skills, and knowledge of how to wire the modern alternator to a 60 year old car.