I do realise that Jim.
The point that I was trying to make is that not everything is bolted down, i.e. with bolts requiring spanners to remove, especially if it needs to be removed in a hurry.
Incidentally I do have an unmolested spare vale case, in my collection, which looks similar to the one which I posted pictures of in post 14. When I got it I did check it against the known dimensions of the Thompson 20 rnd mag box and they were a little different. It is possible that a different spare valve case was used for the Thompson mag box or a the size of the Thompson mag box varies.