Here is a weird thing I've seen in the past on '66 Imperials (and perhaps '64 - '65 cars, too) - Some heater cores have one inlet/one outlet, over against where the cowl and RF inner fender meet up. Others have those and two more out the bottom of the heater box, under the hood. Mine has the two, as described, with the two other holes on the bottom of the heater box under the hood plugged off with no connection to anything. I'll post what I have this evening. What say you?
