I'm expecting you to have a rail alignment piece at hand - if not you can find one e.g. as "rail_too.stl" at https://www.thingiverse.com/thing:3247870/files or at https://www.thingiverse.com/thing:2804412 You will also need one " Tronxy x5s reinforced left motor mount by xxdanmurphyxx" from https://www.thingiverse.com/thing:3200434 - AND ONE OF THE MOUNTS NEEDS TO BE PRINTED MIRRORED! Besides threaded sleeves, idlers (eight with teeth, two without), a belt that is still long enough and the usual mounting material (M4 screws and T-nuts for the 2020 extrusion) you will need M3x16 screws and nuts to mount the idler plate to the gantry plate (also M3x20 if you want to add the X-profile-brace) and for each axle an M4x16 and an M4x20 screw. (Cylinder- or pan head prefereably.)