I found with orange that you needed to tell them all of the bike models that used the same part, and there were a few I think that used essentially the same rear end.
Yes, there are 3 plastic parts, i will have to study pictures of the models from that era and see what looks likely.
I'm surprised that orange have nothing, even going back over 20 years, my experience with working for British engineering companies has been that nothing is ever thrown out.
Interesting, the items in your photo are different to the three X1’s that have passed through my hands, the plastic part has either been one piece or in two halves but always just the simple tube like in my link, only the metal inserts had the built in top hat.