A simple pair of indicators that show that your X-Axis is still lined up.
Fit the indicators - make sure that the one on the leadscrew is high enough to avoid clouting the fixed indicator. Don't snug down the one on the leadscrew yet.
Line up your X-Axis (this https://www.thingiverse.com/thing:2992448 will help) and then adjust the indicator on each leadscrew so the pointer lines up with the fixed indicator.
You can then just use a Mk I Eyeball whenever you feel the need to check the axis is still in alignment (hint: jogging Z at 0.1mm per click on the control knob is useful).
 - You'll need to partly remove the lead screws to fit these and I wouldn't have bothered if I hadn't had a cracked connector (a ticking sound on Z moves was the giveaway). Lulzbot use locktite or similar on the connector grub screws and I needed to use some heat to break them loose.
So the process is:
- Jog the X beam to the middle of the Z travel(ish).
- Undo the leadscrew connectors (just from the leadscrew; you can leave them attached to the motors.
- Remove the printed top Z plates from the frame.
- Lift the X-Axis so the bottom of the leadscrews are exposed and remove the bottom bearings.
- Pop the leadscrew indicators onto the leadscrews (I'd fit the M2 clamp screws & nuts prior to this).
As all the good manuals say, assembly is the reverse of the disassembly.