Blimey, now we are into exotic/specific questions !
The Factory Parts Book(s) will hold the reliable answer to that one.
I'm not sure I've seen one, do they exist ?
Eyeballing the brochures, they all look very similar.
Lets see if we can link to the picshttps://cybermotorcycle.com/gallery/Norton-1930/images/Norton-1930-16H.jpg
I don't know if its any help, but a while ago I came across someone who was making a range of replica racks,
for quite a variety of bikes. He said he was having difficulty in obtaining the right tubing, so was thinking of giving it away.
He'd be closer to you, that might be a good avenue to investigate, since I'd think that oem racks might be tough to find these days ?
P.S. If you know of one, grab it !
It doesn't take much to add or subtract a bit of tubing to make it fit, even I can weld enough to make it neat and pretty.
And if its too different, it would serve as a good pattern to get a 'correct' one made.