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As I mentioned to you earlier I haven't come across a Grid tool that lets you create grids where the length and height is not the same.
Here's one option for you:
I hope this makes a bit sense to you
I was racking my brains trying to think where I had seen a dialog to create different horizontal and vertical spacings - It's in the Gridline function! Add Gridline to Map allows you to enter different spacings.
Alas, these are just lines and you cannot select, copy or snap to. If only.....