The Mark X is a large ring mauser just like the 98 mauser is a large ring. Any prefit barrel intended for a large ring mauser will fit either the 98 or the Mark X. If you have trouble finding the chambering, barrel profile, and twist that you are looking for in a prefit barrel, you can simply purchase a contoured blank with the desired features and have it threaded and chambered. Final cost will be about the same.
In terms of parts compatibility, there are some differences between a Mark X and a 98 mauser, though most parts manufacturers will not make a distinction. The Mark X uses different scope mounts, uses a trigger with a side safety, and has different bottom metal. The different bottom metal will mainly have an effect on stock inletting. For instance, the B&C Medalist stocks with aluminum bedding blocks are inletted for commercial bottom metal. The Boyd's laminated stocks are inletted for military bottom metal.
In comparison to a military surplus action, the Mark X's need very little gunsmithing work done to them. Send the action to a smith of your choice, have the bolt locking lugs lapped, the bolt face and receiver trued, barrel installed and headspaced, and the desired finish applied. When you receive the barreled action, drop it in a stock (glass bed, if desired), mount your scope and go shooting.
For barrel and action work, I recommend Mark Skaggs. Here is a link to his website:
If you follow the above prescription, you will end up with a good, solid, working rifle at reasonable cost. If you desire a full custom, that is a different ball game.