I did some research and came with a bulletproof combo for Optimus Waterblocks. Most backplates required 3rd party hardware or sat on top of the stock backplate which introduces more flex to the overall assembly.
GENNEL Metal LGA1700 Motherboard Backplate, CPU Radiator Base Heatsink Mounting Backplane for Intel LGA 1700
Amazon.com
Thermalright Contact Frame
The backplate accepts the included M3 Optimus Mounting Hardware and also fully replaces the stock backplate. It accepts the #6-32 screws from the Contact Frame creating a very rigid and flat sandwich which prevents any bending. I think mechanically connecting the various layers with equal clamping forces is key.
I’m in the process of lapping my 13900k IHS and will report back with before & afters.
I may pickup a cheap 12600k for de-liding and direct die testing. I think it would be possible to modify the contact frame slightly and use it as a shim.