Usually a XP 100 thread will also be relieved where the guard screw comes into the receiver ring. You don't have that problem with a 700 or 722 action as the action screw comes up between the receiver lug and the end of the barrel tenon. If you look at a factory XP-100 barrel it will just have four or five threads behind the recoil lug. Since your XP action is glued into a sleeve, then that's not a problem. However, the tenon from a barrel from a 700 with a recoil lug will have to be shortened for your action without the recoil lug. The bolt nose recess will have to be set back the thickness of the recoil lug, threads will probably have to be extended as well as you lose the relief provided by the recoil lug. The first thing you might want to do is to screw the barrel into the action and check to see how the barrel threads fit with the receiver threads. It wouldn't surprise me that the XP threads might have been trued opening up the threads when it was glued into the sleeve. If the threads have been opened up, then a barrel that fits the threads for a unaltered 700 could be too loose. It just depends upon how far out of line the original action threads were before the threads were trued. Screw the barrel into the action and see if the barrel has very much shake. If it feels pretty tight, then the threads in the receiver probably weren't trued. If it feels pretty loose, then it probably was. The difference between a tight thread and a loose thread is the amount of clearance between the thread flanks when the barrel is tightened. They will both have clearance, the loose thread will just have more. If the threads feel too loose, then it would probably be best to cut the old threads off, rethread and rechamber if there is enough cylinder on the barrel to allow this.
FWIW, when you start having to do too much to the tenon and headspace to get the barrel refitted to the XP, you won't be too far off the cost of a complete new threading and chamber job. When it gets to that point, you have to look at whether you would be better off to install a new barrel and forget about reusing an old barrel. There's a difference between paying to have barrel work done and when you can do it yourself. Lots of things that you can afford to do if you are doing the work yourself, become unfeasible if you are paying to have the work done.