For readability, I have set up the following custom formats, using a
non-proprotional font (Courier New) and right horizontal alignment
with zero indentation:

#,##0" "
"[ "#,##0" ]","[ "-#,##0" ]"

(There are two spaces between quotes, or a combination of one space
and one square bracket.)

Thus, cells with normal numbers line up with numbers enclosed in
square brackets line. That is, the right-most units digit and the
comma separators line up.

Additionally, I want the column titles (dates or text) to line up with
the right-most units digit of the numbers. I tried the following
custom formats:

mmmyy" "
Text" "

The date format works well.

But the text format fails. The text is flush with the right-hand cell
wall instead of being two "Courier spaces" to the left.

I have worked around the problem by using normal Text format and right
horizontal alignment with one indentation instead of zero.

But I don't know if I can count on one indentation being equal to two
"Courier spaces".

(If I can, where is that documented?)

I would prefer to use a custom format that is similar to the others;
that is, something following by two spaces in quotes.

Can someone tell me how to do that?

And if there is a better way to do this altogether, I am open to
different approaches.