Age of TAPPAN furnace

I need some help with the age of a TAPPAN furnace, serial # 78B06013b,model # HGF100D36 - TAPPAN AC serial # 77C21255, model # CM-24-43-C.

Thanks for all the help!!!

Tech guide = Furnace Feb. 78
A/C March 77

Jeannot

Thanks!