KevinAKASam has produced a number of linear rail mods for the ender 3 that have been absolutely great, however the only option for linear rails on the Z axis was for the belted-Z mod.
The parts provided here allow you to add linear rails to an ender 3 with single or dual Z motors, barely modified from KAS's original design to support standard leadscrews. I highly suggest pairing this with oldham couplers to make any Z-wobble negligible. the motor mounts are not the best but they work. I saw similar floating around and thought I could do better but ended up pretty similar to everything out there. Anything that lets you mount the motor away from the upright 2040 will work.
Yes I know this is cursed. Belted Z is the way you should go if you have an ender without any mods yet, if you already have Dual-Z'd your ender like I did this helps prevent buying a bunch of new hardware, if you want to linear your Z axis.
This goes together really easily, especially if you look at Kevin's docs and CAD for reference.
The author remixed this model.
remixed for dual leadscrews instead of belts.