If you swap out the radiator, you will also need a coolant overflow bottle, a newer style ('92+ I think) heater control valve for the new piping, and will need to address the coolant temperature sensor (your sensor is currently in the radiator, where as the open systems use a different type sensor in the thermostat housing). Check the FAQ sticky... there are sever comprehensive articles on how to do this.
There are actually easier ways to to that as well that don't require all the new hardware (its all in the FAQ).
-2001 XJ Limited, 4.0L, NP231 w/ SYE, AW4, 4.5" Lift, 32" tires, 4.56's
-1987 XJ Pioneer, 4.0L, NP231 w/ SYE, NV3550, 4.5" lift, 4.10's, D44 rear