which cisco routers can use the dsu or csu card
The 60 pin serial connection is just that a serial connection. Normally this port connects to a CSU/DSU. The wic card in the 2620 is actually a DSU card made to terminate an actual T1 that is why it is RJ-45. So you would need something like a WIC-1T to put in the 2620. Then you would have a serial cable on both sides. The issue you have now is that the cables ends are different.