This ended up working out very well. I made a couple adjustments to the hardware requirements:
The middle M4 bolt should be quite a bit longer than 14mm, closer to 20mm is better, otherwise, only the tip is engaged. You will not need all 20mm of course, but it will prevent the issue of the bolt accidentally being disengaged from the nut through excessive turning. This will allow a much wider range of tuning for tension without having to be so precise on the initial lockdown of the belt mount. The reason for this is, with my set up at least, it requires bed disassembly to adjust the belt tension under the plate. If I can just loosen the idler, shimmy my hands under the plate and move the belt loosely, then retighten the idler, I can adjust tension or even change a belt without taking the bed apart. With the shorter bolt setup, it requires a great deal of force and tensioning under the plate, which means it can't be done by one hand or in a confined space. The longer bolt will allow it to be done with one hand and in a confined space.
I used 45mm M3 bolts + Nylon Lock nuts + M3 washers on unthreaded spacers to retain the Idler Body in case of M4 bolt failure. I used these spacers from Home Depot: https://www.homedepot.com/p/Everbilt-1-in-x-1-4-in-Nylon-Spacer-2-Piece-814928/204276568
- I had to drill out the spacer holes a bit with a 5.5mm drill bit to get them to slide smoothly.
It works great and one of the better mods I've done to my printer!