Any question answered...

Odd that it doesn't match their own stems. I'm using one with a 3T ARX and it's a perfect match for height. If you have the equipment to cut it down accurately and without distorting the shim I'd say it's ok to do that, but it would probably be preferable to find a shim the right height.

I reckon our workshop manager will be able to do it using some kind of saw and a 1" steerer tube or something similar to keep its shape.

As you say though, it is odd that it doesn't fit the stems it's apparently designed to work with.