LevelX and ULT work independently of one another. It would possibly be easier to tune the L10 if you had a stock RT on/off, but if not, just take all of the shims out of the ULT and start tuning the L10 first.
For the L10, remove all shims from the L10. Use the largest carrier you can that does not leak. If you switch down to a smaller carrier, use the same O-ring. The carrier size is designated by dots and rings. Dots are 1/2 sizes, rings are whole. This is in the first post in the L10 thread in the sticky section.
Once you have the L10 tuned, you can start tuning the ULT. One tip, tune the L10 without the detents if you have a ULE body.
Also, as mentioned, not all X valves RT well with only 850psi. Some need 900+.