Hi, a quick update. I've received the spacer and shims today and was able to install the flash hider on my MR762 with this following parts:
Shim Kit 71657-1 .750OD x .635ID
Spacer 71734-1 .750OD x .635ID x .125
I ended up needing one red shim and 3 non-colored shims. Unfortunately I can't tighten it down as my Magpul armorer's wrench is too thick (as are my open ended and crow foot wrenches) but I think this is the right solution.