Here are Cable Drum Wagons converted from Conflat L wagons. They are drawn full size so shall need scaling to suit your model.

Two separate designs of cradles are drawn. The triangular type seems the more common. The frames are drawn from photographs so I cannot vouch for the exact dimensions as I couldn't find a suitable diagram, but they look ok to me.

Brakegear can be found with the Conflat L files and buffers elsewhere in my designs.

The photos show a short electrification train.

Enjoy

Jonny