Check your passenger rear door jamb for the factory vehicle load and tire inflation sticker. If it is still there, it will list the factory recommended sizes. Also check this thread: http://mmb.maverick.to/showthread.php?t=44876 for more info.
Todays equilvalent is a 195 75R-14. It's about the same as the c78-14 that was stock. You can also run a 205 70-14 on a stock rim also. My Stallion has BF Goodrich tires in that size (205 70-14).