There are also two groups of photos on Smithsonian.
https://americanhistory.si.edu/collections/nmah_1301514 and
https://americanhistory.si.edu/collections/nmah_751254First one look like some rough prototype, but has a straight image of board conductors, albeit in very poor quality.
My goal is to try to build a clone of Halarc ballast for fun. Hard to get a proper DC lamp, but I suspect a regular modern cheap Chinese NaSc lamp of Venture style will work on DC at least for some time. Schematics looks rather simple. I can ID a classic looking ignition transformer, some diodes (may be also ignition SIDAC), one single small plastic transistor or SCR in TO92 case, a larger transistor or SCR in TO220 on that prototype board, a large electrolytic of 50uF, couple of power resistors, some small capacitors, and one or two thermal fuses.
By the way, what happened with James' Lamptech site today??