1974 Brain Box saves the day.

See that diode? Black component on board. I bet thats directly hooked up to emitter (pin 3) for back-emf protection. So it looks as if the flow to ground is from the collector to the emitter just by the way the band is pointing. You can really make the entire case an isolated heat sink if you make a dedicated ground strap off pin 2 and isolate the TO-220 heat sink (also pin 2) off the case by the mica insulator that way it can still pass heat to the case but it won't be conductive to the case. The TO-220F is a plastic insulated heat sink model of the TO-220