I believe the shell is a original British para shell but the chinstrap rivets has been added to it post war.
Time for you to see then :-)I'm not convinced that it's converted for use as a Para helmet, I think rather it's the other way around. I'm basing this supposition on the fact that I've never seen any with either of the airborne chinstraps (not even a Danish version), but I have seen a couple with the standard infantry/RAC chinstrap fitted.
This is one I have which was also found here in DK.
Nice helmet Alex!