I've decided to tear into and engine thats been sitting in the garage for a year or so...getting heat from my girlfriend about "finishing what you started."

It's stamped as follows: C8OE-6015A code 8E20 here's the question as I decoded it:
C=1960s era
8=1968
O=fairlane/torino
E=engine, engineering
6015=??????
A=289/302 cid
8=1968 stamping
E=month of May
20=20th day
Is it possible that Ford, in Metuchen, NJ, had put a engine slated for a fairlane/torino into a mustang with a C-4 tranny? Is this common place in mid-year production models? or did the mustang the engine/tranny combo came out of suggest a donor history, ie. non-numbers matching

Thanks for any help