Hi mylchreest,
As far as I know, the WIC-1T cards are designed to go from Cisco 60-pin "5-in-1" connectors to RS-232, RS-449, V.35, X.21 or EIE recepticles. If both 1603's have WIC-1T's in them, then you want a double ended Cisco 60-pin "5-in-1" connector cable. Whether they exist and where you can buy them from, I have no idea.
If you want to simulate WAN conditions, try connecting the WIC on one router to the S/T ISDN interface on the other using an RJ-45. That'll work too.
Hope that helps!
bdx