Hmm interesting.

Don’t know if two picture might illustrate the point better. I found these via Google image search.

Physically they look identical but the main differences I see are that on the RAF version you have “Artificial Horizon” painted around the bottom, the “U” shapes on the 9 and 3 o’clock position on the dial and the double line for the horizon indicator.

This is why I wondered if in fact the RAF version was the same as the US version.

(RAF left, US right)