I bought old vintage back when they were cheaper pens.... I started at M and went wide, and by the time I went narrow. I found the '50's F narrow enough (Half a width narrower than modern Pelikan or MB..(same width as modern 200's nibs))....did get a couple EF's. Semi-flex.
I liking wide nibs once more than now, never had a need to make a narrow nib . I did eventually bought some narrower nibs........very good nibbed pens.
One of the advantages of semi-vintage and vintage pens is the better nib than modern .... on the whole.
So by me, I have no reason to grind a nib narrower..............but when one puts tolerance, that a Skinny M can exactly match a Fat F of the same company and era, and other companies made wider or narrower standards of with.....none are going to be exact.....1/2 widths being 'normal'.
They made nibs to their own company standards back in the Day of One Man, One Pen.....Parker users were trained to want a fat M, Shaffer was trained to think a Fat F was M. That prevented scarce customers who bought a new pen every 7-10 year from making horrible mistake and buying another brand.............which could have happened if Parker made Narrow Shaffer nibs.
A wet or dry ink can make up to a 1/2 a width in your writing. A slick paper can make you nib write 1/2 a width narrower.
On cheap 80g copy paper your nib will write wider.
So insisting on only an exact width of your nib....will deny you joys of different papers and inks.
If you have some good paper.....go to Richard Binder's site, he has a print out chart of width that you can measure your nib width too.
As I said, I don't think grinding a nib narrower is a skill one must have, but many do. So have fun....Pelikan 4001 is a dry ink...in you don't list a flag, I can't tell you to buy the Blue Black.....if you are in the States, you could smuggle it in....It is a very nice dry ink....one of the very driest.
You will have to stay away from many Noodlers inks. Once before Noodlers inks came on the market Waterman was considered a wet ink. Now some Noodler users consider Watermann a dry ink. .
Oh a narrow nib is no good for two toned shading inks.....which needs 90g or better paper as is.
What ever you do.....don't use the feather champ....Ink Jet Paper.