Quite uncommon, but lucky for us, all of the signals are on the single MIC connector:
The pinout for the homebrew cable is this:
MIC pin #1 (MIC) → 3.5mm TRRS ring 1 (RIG_AFIN)
MIC pin #2 (PTT) → 3.5mm TRRS ring 2 (PTT)
MIC pin #3 (DWN) → NC
MIC pin #4 (UP) → NC
MIC pin #5 (8VDC) → NC
MIC pin #6 (RX OUT) → 3.5mm TRRS tip (RIG_AFOUT)
MIC pin #7 (MIC GND) → MIC pin #8 (GND)
MIC pin #8 (GND) → 3.5mm TRRS sleeve (GND)
Manual can be found here.