FYI, PD4104-4787 was part of a 84-bus order for Western Greyhound Lines, HQ'd in San Francisco, CA. This order was delivered between May and July of 1960, and your coach's original fleet number was P-7614.
FWIW & HTH. . .
PS: Please take a couple of minutes to edit your forum profile with at least a signature line similar to mine below. Simply click on the Profile tab above, when the next window pops open, click on Forum Profile Info in the LH menu and follow the prompts. By doing so, it will better help us help you with sources for parts and service, plus you might discover you've got a fellow busnut nearby!