I've done this swap, but my memory aint great. I'm pretty sure the lines were the same size, so I don't think you'll need an adapter. I used my MJ prop valve though so I could be wrong.
IIRC, You should have two lines going to the back of the truck. One that goes through the valve and one that doesn't. When you switch to your XJ valve, you can only use one of those two lines to the back, because one of the holes in the XJ valve isn't active. So, when you choose which line to use, make sure you use the one that doesn't go through the valve. The other hole in the XJ prop valve should be plugged, because it doesn't work.