Oddball 1970 Dart GT Find....

My '71 Dart GT was born with a 318 according to the fender tag, but it now has a '72 casting 340 in it. An old Chrysler dealership mechanic (he and the dealership were both old) told me the '72 340 ci in my Dart was in all probability a dealership crate engine they kept on hand in case anyone blew up an engine while it was still under warranty. They would replace the blown one with one of these crate engines, and chances are whoever blew up the original 318, which were fairly easy to over rev and damage, had the dealership install the 340 instead of another 318.
No proof, just common sense and conjecture @ this point.