Thanks for all the info on this GH web, I finally completed the final step of restoring my IBM Model F122 (after Soarer's converter, ANSI-Mod and so on) by replacing its case with one of the 1988 M122 (not old style). I want to keep the original F122 metal backplate so only the M122 top shell is needed. This means there is no 3-step legs, but I'm fine with that.
I forgot to take pictures during the grinding process, but there are not many spacers cut off (top and bottom). The whole process take about 1 hr.
IBM Model F 122 is my long-time favorite keyboard. I'm happy to keep it work flawlessly and beautifully with modern PCs without worrying about scratching or damaging the housing.
Sorry for potato quality pictures.