Although I don't have the diagrams in front of me, I believe those external lines go from the ECU to the DCCDCU (control unit?) and are actually unrelated to anything engine related. If that is the case, then they are used exclusively for the DCCD and are unneeded if you do not use the transmission.
B134, 23: this is the display in the gauge cluster tell you what position the DCCD is currently in (ie: Auto, Manual + position)
B136, 28: this is for the Auto setting on the DCCD to help determine when the car is under acceleration
B137, 20: this is for OBD-II, Subaru SelecMonitor, or some simplistic testing in order to report error codes
These are just guesses, though, so I could be wrong.