Motor(s)? It should be one motor unless you have something different than the common Harrison Heaters. If yours is not a Harrison, I am not sure if the motor I linked to is the correct motor(s) for you. During at least through 55 first series heaters where a dealer option, not from the factory. Most were one of two models. Harrison re-circulating or Harrison Fresh Air. Mine is a Harrison re-circulating model but the Fresh Air model are very similar, they just have extra housing that extends over to the side to pull in fresh air. There should be a diverter that flips from Heat to Defrost.
Here is a photo of my heater:
Harrison recircultaing heater
