Why not call the dealer and ask them the cost for a "new" water pump. You may be surpised how competitive they are. I think I checked and it less than $60 for a "new" water pump from Chrysler. I recall seeing those options on size also on a web site. I ended up with a water pump fromehescosc.com water pump and they did not ask me the hub size question but it fit fine.
The water pump I pulled out of XJ had an impeller like the one in this picture
http://www.hescosc.com/HFW.html The replacement water pump had the aluminum impeller.
If you look at the water pump there should be a casting number on the part where the lower radiator hose attaches. It will be facing forward so should be easy to read with a flash light. Just write down that number and then go to the parts store and see if the replacement pump casting has that number cast into it.
Also I highly recommend you buy the water pump gasket from the dealer. It comes with RTV pre applied and instructions to include the torque on the bolts. I'd also pick up a thermostat at the dealer and swap it out, it will come with a gasket but you may want to pick up some extras gaskets to have around for the future. The thermostat gasket was less than a buck and the water pump was less than $5.
I can try to dig out my old water pump tonight and measure it for you if you like.
I have come to the opinion that new water pumps are not that expensive so I always use new. A rebuilt was rebuilt because something happened and my luck the casting is messed up.
If you are changing the water pump I also highly recommend changing the idle pulley by the AC compressor, should run $10-$15. Also check the bearing for the mechanical fan it could be rough. If you need to replace that it is a $75 dealer part, have to buy the bracket assy to get the new bearing.
