I upgraded my Hypercube 300x300x300 (https://www.thingiverse.com/make:332719) to use linear rails based on the BLV Fusion work by Ed. In addition to the X & Y conversion I also switched to linear rails on my dual Z setup. This necessitated adding a set of idlers to bypass the rear vertical 2020 rail support as otherwise the belt would rub on the extrusion. I simply used one of the existing idlers and it worked perfectly.
I also had to design my own front plate as I'm using the Zesty Nimble V2 Beta on my Hypercube After several iterations I finally came up with a version which uses some of the bits from Zesty as well as many of the parts Ed designed. I'll post all the custom and remixed parts once I'm completely done with the upgrade as I still need to print a set of custom bed mounts in order to keep the 300 height.
The only downside to the conversion is that I lose 35mm in Y due to the added depth of the carriage over the basic Hypercube design. I also lost 5mm in Z height but will regain that once the bed mounts are installed.
The Z linear rails were a challenge due to the limited space and not wanting to lose any more in Y than I already had with the XY conversion. I modeled everything and printed new Z motor mounts in order to lower the Z motors and also reworked the Z bed mounting system to work with the rail facing sideways as well as accommodate the revised motor placement.
Linear Rails: I used Machifit linear rails all round and am pleased with their performance. They required very little in the way of cleaning with IPA before sliding freely. After flushing the carriers and drying them I then lubed them with Super Lube Multi-Purpose Synthetic Grease. One of the rails didn't move as freely as I would have liked but closer inspection showed that there was a bit of extra material on the red wiper that was dragging. Once I trimmed that away it slid freely from end to end.
All the printed parts I used/modified/created can be found at https://www.thingiverse.com/thing:4068795