This question has been asked before, but it appears it was never answered.
Is Ghost Master on GOG the US or UK version?
I ask because I want to install the Ghost Master fan-made patch that allows you to use any of your ghost on any mission, and the installer ask you to identify the version.
You can find this patch at ghostmaster.net
Also, I just wanted clarification that the bonus level is in-fact included in the GOG version of Ghost Master.

Hello,

Saw this topic in passing whilst hunting for widescreen information.

While I don't know the answer for certain, I can say that the UI text files use spellings such as "colour" which implies it's the UK version as I would assume that if it was US English it would be "color" etc.

As I said, it's not really definite but hope it helps (or at least the next person with the question given the age of this topic)

I have no idea one way of the other re the bonus level; I haven't gotten too far in the game yet.