I was trying to make an 83-key XT keyboard layout diagram on
http://www.keyboard-layout-editor.com/ late last evening, but I came across several problems when I was trying to align the backspace key.
1. If a normal alphanumeric block was 15 keys long, then backspace needs to be 2 keys long, since the top row has only 14 keys.
2. The second row has tab (3/2) and a slightly enlarged right bracket (5/4?), but they need to line up with the third row to make room for the return key, which is 2 keys tall and 1 key long (since it aligns with the PrtSc key), meaning that Ctrl needs to be 7/4 keys, instead of 2 full keys long.
3. If the alphanumeric block is 15 keys on the XT, then the right bracket needs to be 3/2 instead of 5/4, since the size of tab is fixed by the offset of Q.
4.This means that the alphanumeric block is only 14 and 3/4 keys long on the XT, and the backspace is only 7/4 long, not 2.
5. But I don't seem to find a measurable difference on the actual backspace key and the 0/insert key, which I know for sure is 2 keys long.