I believe you need to just replace the hoses and heater valve with parts from a 91+

 

One other thing.....if u use the existing pressure bottle, the cap on the bottle needs to be vented so coolant level can easily rise/fall as the engine heats/cools (no pressure in the bottle). There must always be some coolant in the bottle, even when the engine is cold. If the bottle runs dry, air will be sucked into the cooling system, which defeats the purpose of the self-burping "open" cooling system.

I believe the vacuum operated heater valve can be eliminated if desired by using longer heater hoses connected directly to the heater core, t-stat and water pump nipples. Vacuum line need to be plugged. The vacuum operated heater valve was eliminated by the factory on '97 up XJs.

 

I found this thread by searching but I can not get the picture to load. So I have a quesion related to this. I was "given" a new radiator unfortunately it appears to be from a closed system. On the side of the radiator that normally (on open systems) has a fill neck at the top, this one does not. However, about mid-way down there is a plug (about 1.5" dia.). I'm wondering if there is a pipe with a radiator cap that I can thread into where this plug is to use this in an open system vehcile? It would have to elbow out and come up to the same location where the cap would normally be. Is this what was in the OP's pic?

I'm hoping I can put this radiator to use since its brand new, but obviously want to keep the open system my '97 came with. My budget currently doesn't allow me to purchase a new $140 radiator at the moment.

 

Does anyone else have any pics like this? Thank you