Just a follow up to tjjp77, a friend of mine has a RB1 in his 2005 jeep rubicon.
Yesterday we were discussing if his RB1 would fit(play) into my 2003, so he removed it from his jeep(nice guy) and we plugged it into mine, worked perfectly. His RB1 is the one that ends in (AH) #P56038629AH and has the same connectors.
In my search for a proper model number for my 03, some sites indicate that it is not compatible with my 03, wrong.
So I can for sure state that at least the one used on the 05 WILL fit the 2003, just make sure it has the "21" pin connector, hope this helps