Thanks Andrew (fink) for your help! The Printrbot wiring specs in this thread are confirmed on my Printrbot Metal Plus. They should work on the Printrbot Metal Simple and even older wooden Printrbots as they all use the same wiring that Andrew noted.
I bought this connector (recommended by someone else in this forum, but different thread), cut it and soldered my Discov3ry wires to it, and swap out the Printrbot filament extruder and my Discov3ry extruder by unplugging and plugging in each extruder depending on which one I want active.
I have a paste extruder tip 3D model that mounts to the Printrbot v1 metal extruders using the existing screws. I will post that model in next 24 hours as I've taken it through a few iterations, successfully printed it already and think it will work well.
On the software side, I've been successful so far with Cura with M302 (allow cold extrusion) to get the extruder hooked up and functioning. Now I need to start testing materials and actually printing!