Fan Blowers

[Zeroman]

Hello,
I am working on my heater blower and have these two available to reinstall. Can someone enlighten me on the difference between the two? The plastic one is out of my car, 69 Charger with AC.
The metal one I believe to out of a 66 Belvedere. Aside from the material they appear identical except the plastic one has 31 blades compared to the metals 28.
I'd like to use the metal one but also want to make sure I'm moving as much air as possible. As it is the two outer registers hardly blow. The center one blasts air but not the ones at the ends of the dash.
Thank you,

[Bronzedodge]

As an HVAC guy I can tell you this:  The important things are diameter and width.  It cannot rub the housing of course.  If they're the same, no worries. The only other thing would be the weight, the heavier one will draw slightly more amperage, and a bit harder on the bearings.  Never seen a Mopar fan motor fail though.

[DanielRobert]

Just went through this. My car has a/c and the wheel was thinner. The thicker(or deeper) one was rubbing the inner parts to the housing.