While helping a friend with a QUBD OneUp printer and looking for a solution to a sagging stock X gantry, I couldn't seem to find a complete solution. Most available parts were designed for the TwoUp and would limit the printer to half of an already small build volume.
I did end up finding a remix of a fairly decent TwoUp gantry upgrade that started to address the loss of X movement. Starting with those two designs, I tweaked and modified them to allow for what appears to be a complete range of motion for the heated bed and the stock hotend using this extruder/hotend mount and this x carriage. I then created a Z mount that opened up the area and hopefully will not limit downward travel.
Assembly requires M4 hardware as mentioned by the original source material. It also requires a bit of patience while tightening things down during assembly to avoid excessive part warping.
Overall, I'm very pleased with the effects of this upgrade on the OneUp printer. The gantry now feels very solid.
.2mm layer with .5 nozzle
Printed with Inland Orange ABS at 235° and a bed temp of 95°. Bed surface is stock glass with glue stick applied.