I went ahead and bouth the heater core from O'Reilly's. Box says Ready-Aire by proliance, made in Mexico.
I purchased the heater box rebuild kit from Detroit Muscle Technologies (based upon ya'lls recommendation. And I noted to them that you did).
Last summer I rebuilt the actual carcass of the box- sorry, still no pics.
My wife is visiting her family in mid-December w/o me (
)
Gonna use the time to put it all together.