Try going here they give a breakdown of the
http://www.fiatparts.com/
I don't know how similiar an 84 and a 74 are but..
I just had the wiper motor go out on my 1984 Spider..to get to it (where the hose are) I had to remove the lower windshield chrome piece, then the metal wiper panel (you can leave the plastic vent on....if the '74 has this) pg36-37 in pdf file.
As for the heater fan...I read somewher that if you can manually spin it and its possible it'll start working. And to prevent further seizing run fan periodically.