I see your point. In the Year One catalog, both emblems are listed as correct for 1973 Challengers.
Paul Herd´s Parts Interchange Manual says that the 340 four barrel emblem is correct.
I have a couple of pic´s also, but it is hard to say something definite, but it does more look like four barrel emblems than magnum emblems to me.
Maybe this link can give something if you have sharp eyes or if you can zoom in the pic´s.
http://challenger.mpoli.fi/forum/viewto ... 2931#12931 Good luck!