The Z1 battery is used for the scale lamp / dial bulb.
A Pritt tube seemed about right, but not enough clearance for C cell
I replaced the card insulation with marge tub lid. It's needed because Alkaline batteries and Zinc Carbon have opposite polarity cases and the insulation film on Alkaline easily torn and then body (+) shorts to base (-).
The top uses three disks of thicker plastic. The lower two have two coffee tin triangular sockets, the smaller one shorting to case and the fatter one rests on battery top spot.
Solder blobs on inside of the coffee tin case (join is soldered along vertical) act as locks and contacts. hence the lower discs cut. You push cabled plug into "socket top" and set it in with "flats" at the blobs and give a 1/4 turn using the radio plug as "key" to lock cap.
The inset bottom disk has a strip/spring (all coffee tin) soldered on before it's set on the card spacer and soldered.
I couldn't find any decent quality scans so I retyped most of the text and got the "Zenith" logos off a document rather than a battery.
Anyone wants this I can load it to the technical library.