My HIPO had a scheduled build date of January 11, 1965 and is a Dearborn car. The engine assembly date is January 14, 1965, which goes along with the theory that HIPO engines were built very close in time to the cars scheduled build date (which the actual build date was a few days behind the scheduled build date) and were not left sitting around waiting to be used in a later build.
Scheduled Build = A11
Engine Assembly = 5A14B
Intake Manifold Tag = 5A8
Engine Cast = 5A5 (my 17th birthday)
Heads Cast (both) 4M17
Jack