I love the plan of taking in the local flavor along a trip... But that sandwich shop will have a serious negative impact on your route and it's take-out only though I could suggest a decent park a few miles away.
But in the name of experiencing the best of regional sandwiches, I'd suggest a cheesesteak from the spot Rich mentioned
www.stevesprinceofsteaks.com
Only minutes from the PA turnpike and right up there with the best in Philly. Their website even provides proper etiquette for ordering

My choice is usually Provolone Wit or Mushroom, Provolone Wit. Your choice on double meat and hot peppers from the counter.
If you still need the hoagie fix, I might be convinced to pick up one for you.
David B.
'07 Ural Twourist