Manson tablet catcher

In my pile of projects, I've got a Class 26 to detail. In the cab side is a recess for a single line tablet catcher. Filling this with such a device seems like a good plan but finding out what these things look like is more of a challenge.

Fortunately, last weekend I went to the nearby Great Central Railwayana auction, and guess what I found ?

The device is listed thus:

A Manson tablet catcher locomotive arm. Manson's tablet exchange system was used on the Caledonian, Highland and Great North of Scotland railways. This loco arm came from Inverness but is not marked with company initials. Examples such as this are relatively rare.

It sold (to someone else, I wanted the Isle of Man poster, which I was also out bid on) for £50.

Now, I know very little about tablet exchange apparatus but since I know I know very little, a couple of snaps taken with my mobile seemed like they might be useful and I present them here. The catalogue is included in the shot to give an idea of scale, it's a standard A5 sized booklet. You can draw your own plans from this.

The head is a pretty complex item that would suggest resin or whitemetal manufacture rather than etching.

Needless to say, it's of mo use to me. What I need is a much flatter device like the one shown in this photo taken by Tom Burnham at Thurso in 1973.

Anyone got a drawing ?