I had one on my Zaskar, fit nicely. I then tried to fit one to a '97/98ish S-Works (prob similar to your stumpy) and it wouldn't fit. The dropouts aren't flat and the welds kind of get in the way. If you look at that picture above, the area around the top bolt needs a flat area to sit against as that's where it'll press against the frame when brake forces are applied. That area on the specialized wasn't really flat from memory (and nor is the droput), so the whole thing wobbled about all over the place.
Might be able to fit with some fudging but my best fudging attempts didn't get anywhere.