Here's the situmatation:  The blower fan in my '88 Cimarron is used a lot.  A hell of a lot, with it being hot and all.  Here recently, it has started acting up.  Sometimes when I start the car and turn on the air, the fan doesn't blow.  If I pop the hood, get out, and bump the blower housing with my fist, it starts right up.  Sometimes it takes it a while to get up to full speed.  Sometimes it takes more convincing to start up.  Sometimes it works without a problem. 
 
I've all but determined that the blower motor is going out on me.  I don't know why; I didn't tell it to.  I have the service manual, and it tells what to do, but it doesn't say how many pieces or how long it's going to take, and what part I need to get from Auto Zone to replace it. 
 
Does anyone have advice on how hard this is (remember, it's an '88 J-car), or which motor I'll need (Auto Zone lists a press-on-fan motor and a bolt-on-fan motor)?  Much appreciation in advance!   
 
 
Yes, it has air conditioning.