Turns out that it was originally chambered in 450NE.
I think it is too big an action for the 450 but maybe the next size down '02 Webley action was too small for the 450.
So, if one wanted the '02 in 450, he was faced with a too big or too small action and the '02 just didn't lend itself well for such a chambering.
I'd have to look through the Webley '02s of both sizes and see if there are many 450s.
My supposition is that there are 350s and maybe 400s built on the medium action and some 500s and 577s (maybe 470s) on the large action but there wasn't an action size that lent itself well to the 450.
Anyway, I'm very happy we went with the 500 in that light.