The best I could use as a point of reference was the shape of the taillights.
My reference was "Standard Catalog of American Cars 1946 -1975." The shape of the taillights was the decisive factor. (BTW, Johnny: this is required reading for car buffs like us--endless source of fascinating facts.)
Why we are on the subject. Who owned the Plymouth? One of the soldiers or was it bought just for the occasion?
Logically, either scenario would have been consistent with Mob practice. They probably would have taken it to a junkyard to be crushed, with Carlo in it, or simply have abandoned it in some remote spot, as with Paulie after Rocco shot him.