i didnt realize it was a chain. I have only seen one and it was over by the outlets when I was in western PA.I have eaten at Primanti and it was OK. But, I don't think a multi-city chain qualifies as a dive or diner.
But, Ranelli's in Birmingham (almost on the UAB campus) is definitely a dive. The Richman's Poboy is iconic in the Magic City. Their baked lasagna is only available on Thursday and they always sell out. I think there is parking for 7-8 cars, but not always since their might be 7-8 bicycles there as well. Their sandwiches don't have a bunch of gourmet stuff on them, but they have great bread and very good meat on them. The Richman is 16" long, so you need help with it. My three sons would not drive past Ranelli's without stopping and they have not lived in Birmingham since 1980.
In Indiana PA id recommend:
9th Street Deli (24" steak and cheese")
Al Patti's-A dive that will give you a rib eye on a Styrofoam plate
Culpeppers: Good wings. (they may have go-go dancers as well)
I havent been there in quite a few years now, those places may not even be there any longer.