Is a ford c5 trans pan different than a c4 pan?

YES, if it's the stock c5 pan. The stock c5 pan has a hump in the middle of the pan for the transmission oil pickup, that is the only difference.

However if it is changing or switching pans you are doing, there is some wiggle room. Since the c5 pan has the hump and the c4 pan is flat, you can put a c5 pan on a c4 trans. but you can't put a STOCK c4 pan on a c5 trans.

Why did I emphasize stock? because if you can get a deep enough aftermarket c4 pan think it has to be deeper than 4 inches) it will clear the c5's oil pickup. So in other Words if you get a deep enough c4 pan (deeper that 4 in. I think...) it will fit on a c5.