I always cheated: https://www.ebay.com/itm/DB25-pin-Male-RJ12-RJ11-Jack-Modular-Adapter-6P6C-6wire-Aux-Data-Phone-Telephone-/29186809860?hash=item43f4b1bd44:g:ND0AAOxy06hSGSwC

I had a handful of DB-25 male to RJ-11/12 adapters that worked on all Comdial boxes. Well, that and a Smart Cable SC-88x adapter that read the serial port. IIRC it was always pins 2,3 and 7 and you could use a needle nose to reverse 2 and 3 if it screwed up.