None that I know of. Of course, if it's a different part number than it probably just doesn't fit. Quite likely, a AC equipped car, needing room for the evaporator, has a smaller heater core.
speculatively, GW
R2D2 wrote:
What is the fundamental reason why you can not put
> a heater core that was made for a car without AC into
> a car with AC. Other than geometrically fittings properly
> is there any other reason?