Sorry La Mer, just got off the phone with an old friend of mine who is a Steward. The order would be A,C,B,D. The reasoning is, that if there was no interference to C, then D would have finished 4th. B interfered with C so is relegated to behind C & any runner that finished in between, which does not include D. As B finished ahead of D on its merits & D did not finish ahead of C, then B is placed behind C & ahead of D. D is not penalised by being placed 4th as that is where he would have finished if there was no interference.

Of course he could be wrong, but I doubt it. An interesting scenario all the same.