Hi Dave.
I updated my 5215 chart plotter to a 8616, The GHC 10 autopilot controller to a GHC 50, and the i5601 Yanmar ECU monitor to the GMI 20 display. The installer thought they would all play nice but it turns out the 8616 and the GHC 50 does not play with the downrev Course Computer/Compass. The GHC 20 does play with the older Course Computer so that would have been the cheaper way to go if I'd had known that. The GHHC 20 is now discontinued but I still see some for sale around $500+. I had the installer confirm from his distributor that I'll only need to update the Course Computer and not the 4 connector controller box near the hydraulic pump.
The location you mentioned is I think for the 4 connector autopilot control box. I see that just aft of the pump. I'm looking for the Course Computer/Compass which I think is in the center of the boat somewhere. It has two connectors. We checked in the quarter berth in the right corner where there is an access panel but it wasn't there. So I'm thinking it may be behind the fridge on the starboard side.
-Bill