Each menu has a .data file and a .menu files.  For historical
reasons each line in the .menu files must begin with at least
one space.  I use vim for creating pairs of .data .menu files
from a single list.

I use these commands to add the numbers to the .data and .menu
file:

    %s/^/\=printf('%d:', line('.'))
    %s/^/\=printf('%2d) ', line('.'))

I then add the zero (0) entry manually.  For menus that need
to have more than one column I use visual block mode.  I first
delete and put (p) all the text in visual block mode to pad
each line with spaces so they are all the same length.

This was fairly quick and painless.  YMMVG.