On LGR on Youtube yesterday:
Tandy 1000 PC + CM-11 Monitor! Unboxing & Setup, Clint said "I believe this is a proprietary Tandy connector
that also worked on the TRS-80s".
I don't know if that is true, but it could be a lead.
If it
does use the XT or AT protocol (PS/2 is the same as AT) then there should be four leads, plus maybe a shield.
You might be able to figure out from the circuit board layout which leads are +5V and GND. Then you would have 50% chance of getting the two data cables right.