Short answer : Eminently doable, and since the day will still be young ; and there are lots of subsequent flights PHL-ORD (and it's not so far that an imperfect seat would be insufferable .... Sure, why not?
Longer answer : I haven't come in to PHL recently on 707, but I do arrive a lot on TATL flights (6x in 2011) and have yet to be caught in a customs disaster. But I also sit at front of steerage class (7 usually) and move fast to make sure that my flight is not the line I am standing behind. There are a lot of intl flights coming in at same time, so this is not foolproof; but, and although some of the lines (okay, the line
I am in) move excruciatingly slowly, I can't remember a wait of more than 20-25 minutes, and most were more like 10-15. On the plus-side, the TATL flights often arrive 10-20 minutes early.
Longer answer continued : Luggage. Well, I don't check bags (except when the LH people on preceding flights insist on it
), so I don't know -- maybe others will ; except to state the obvious ... if there is more than just you in your party, the convoy moves at the speed of the slowest ship.
The real wildcard is something I rarely face, which is going back through security. It is a cattlecall ; anyone you missed at passport control will show up again. On the plus side, they are usually pretty good about letting folks on tight connections move through.
I don't see the distance as a big problem to B, or even C.
And, of course, the PHL-ORD flight might be delayed
.
So I would say you are good at 75-90%, and with those odds and .... well, see the short answer, above.