update:
Rather than wait who-knows-how-long for the replacement board to arrive from Tamiya, I closely examined the busted power switch. Pretty quickly figured out it was a DPDT momentary contact switch. So, I soldered up a bunch lead wires under the board (major pain; the board was silicon dipped and my 50-year old eyesight and steady hands aren't what they used to be). Soldered in a DPDT momentary switch, and it fired right up. No good place for the switch yet, but at least I can test things out and keep building.
