I have been looking at the proposed joints picture, fatal on my part to try & make a judgement call looking at a photo
I am thinking that what HandyAndy meant was the actual length of the flat mounting section.
It very much looks as if the rear-most fixing hole will be very close to where the lower shock mount needs to be welded to the wishbone plate ( Sods law says that it will be slap bang in the middle ) !!??
The angle of the joint also looks to be slightly more accute, that said you would be able to loose or gain a degree or Two when fabricating the wishbones.
As TT said, it's worth doing a bit of research on your hubs geometry. If they turn out to be Cossie hubs, why not sell them & use the proceeds to buy some standard ones ? .
It may make life a whole lot easier for you
Besides, I would imagine that Cossie hubs are worth a few £££'s