Jon, I think those two are the same length, but isn't the WW a full round shaft?
From my notes, I think that was the only difference between the two. I believe the full round will fit in the National, however the sewest would have to be very careful to get it in correctly since there is not "flat side" to help "center" it.
On an interesting note, the needles for my Long Arm are full round, and the instructions talk about rotating the needle slightly to advance or retard the timing if needed for problem fabrics or thread.
I think the Damascus Rotary is a later version. After the word "Rotary" got popular. I have older black attachment boxes, most say "attachments" but some of the later versions are marked "Rotary", "White Rotary" and "New Home Rotary". Though when I say "later" it's 1920's or so. I think by 1935-1940 the metal boxes had been replaced with cardboard boxes.
I am more interested with the attachments than the machines, but I need machines to go with the attachments!