Special thanks to snoopy and 7bit.
Jdcarpe, can you post the keycaps needed specifically for the 40%, and add that info to the OP. I'd like them to be added to every future GB.
Sure.
Row 2: 1u Esc, 1u Del or Backspace
Row 3: 1.25u Tab, 1.75u Return or Enter
Row 4: 1.75u Shift, 1.25u Shift, 1u Fn
Row 4 (SA Row 3): 1.25u Ctrl, 1u Win or Del, 1u Alt; optional layout: 1.25u >., 1.25u ?/