HEAT - original vs. aftermarket system.

[Quadrajet]

My aftermarket heat/AC system was in my 72 Suburban when I got it years ago. It never was able to heat the cabin on cold nights to any reasonable degree. Now the blower motor is not working, and it appears as if is this is probably an old (maybe Gen 1 or 2) vintage air system that needs to be completely removed in order to put in a new blower motor. (Vintage Air was not much help in ID'ing what I've got - it seems they just want you to buy a new Gen 4 system..)

Since I already have rear AC, should I just replace the aftermarket stuff with the original heater core and parts? Will it heat better? Did the original systems heat Suburbans on cold nights OK? I'm just not real enthusiastic about doing all that work to an aftermarket system and putting it back in so I can shiver inside the truck a LITTLE less - but indeed the time has come for me to make a decision here..