I dug up the information on the 12v replacement motor for myAD recirculating heater. Harrison model HD-205-54
It is from AutoZone. Part #35512. Everco. The height of the motor is 1/4 inch larger than the original but it fit with plenty of clearance and no modifications. I did need to drill out the original fan to get it to fit the 1/4 shaft with no problem to enlarge it to the 1/4 needed. Here is a link. $29.99 It is reversible also by simply reversing the two wires.
Link to AutoZone part
