What a NICE early 122.

One place to help the 6-volt system along is at the grounds. I'm guessing that, like the later cars, there is a braided ground strap down on the passenger side of the engine bell/clutch housing. Both ends should be free of paint and oxidation at the connections. The same goes for the (positive?) battery cable connection to the body at the firewall.

Any wires on a 6-volt car need to be LARGER than those on the equivalent 12-volt car. Keep this in mind, particularly if you see signs that any wire/cable is getting hot. Someone may have substituted from a 12-volt car, thinking them adequate.

Have you given any thought to converting to 12 volt negative ground? It makes starting easier and sourcing accessories more fun.