Yes, HP does have a DTC cabling manual - at
least they did, I assume it is still available.
It is "DTC Cabling and Racking Guide" customer
number 5961-0373.
Contents include:
 
Part 1: DTC Racking
  <detail omitted>
 
Part 2: DTC Cabling
 
1.  Connecting Asynghronous Devices
2.  Recommended Cables
3.  Most Common cabling Schemes...
4.  Making your own cables
5.  Adapting to Cabling Systems
6.  onnecting to an X.25 network
7.  Supported LAN Cables and Transceivers
 
It includes pin outs for the recommended cables.