[Charlie]

That's a very nice set! That's quite a find.

Regarding your battery, check out camera flash batteries... there was one that was 4.5 volts... I used one to replace a 4.2 volt mercury battery in a Hoffman Trans-Solar radio. The replacement was smaller in diameter compared to the original mercury battery, so I wrapped electric tape around it to fatten it up and it work like a champ.

Battery numbers 531 and 523 are both 4.5 volts. They one is about 50 mm long, and the other is 56 mm long. The 531 battery uses connections like a 9 volt. There may be other battery sizes that will be similar.