As far as the rings go, is the early one one the right in the photo without the extra holes ?
the one with the extra holes i believe belong to> Jag Mk II 3.4 from 179464 and 3.8 from 223056, S-Type, 420, Mk X
IMHO the early one is on the right. You can see the indentations that accept the clips from the snap-on black plastic cover. On the early ones the cover clipped onto the horn ring and you could beep the horn by pressing on the cover. The later cover, which looked completely different, was rigidly attached directly to the steering wheel itself through those extra holes and completely covered the metal. In order to beep the horn you needed to press on the ring since pressing on the rigidly mounted cover accomplished nothing.