qmk_firmware/keyboards/ibm/model_m/yugo_m/keymaps/an_achronism_106/readme.md

an_achronism's custom 106-key layout (107-key if you stick the appropriate keys on RShift and JIS backslash, which are already mapped for convenience).

With the exception of a single extra matrix position between LAlt and Space which only appears on certain later membranes and is almost never actually used, the only unmapped key is the bottom right corner of the numpad (the unused lower half of the vertical 2u key most commonly used as either Enter or Field +). If you like, you can easily add that into the keymap by changing the appropriate KC_NO to whatever you want.