Bell System Wood Box/Case?

[MagicMo]

I have 3 of these boxes from Bell System and I am wondering if anyone knew what was supposed to be inside them? It looks like the left side fits a 500 (with the round feet) perfectly, but what about the bottom cut outs for the right side? It is much wider. I cannot figure it out.
Thanks
Mo

[rdelius]

This might have held one of the portable magneto sets with the handset that fits inside