A Renishaw TP-20 extended force touch probe was purchased. It came in two parts.  The two parts mate together with balls, slots, magnets and spring pins.  I cut apart the base part and was able to use parts from it to make a mechanical adaptor.

I found the pin on the BeagleboneBlack in the pocket nc that's hooked up to the tool height probe signal.  I ran some G38.n gcodes, general straight probing gcodes.  They all responded properly if I pushed the tool height probe by hand.  I determined that by pulling down pin 22 on the BeagleboneBlack the probe signal could be actuated.  I bread boarded a circuit to pull down the pin and to interface to the probe.

I ordered some connectors.

The next steps are to add transient voltage suppression measures into the circuit, to make the circuit more permanent, enclose the circuit (probably will make a new cover for the PocketNC electronics bay), and add strain relief on the probe end of the probe cable.