hi Steve,
I don't have any design numbers, but there are plenty of british built cars which used XJ6 control arm.
you could contact the british club
http://www.clubcobra.co.uk/
or place your wheels mounted to the hubs, with upright and control arms and weld the missing chassis brackets.
get your lower control arm level at ride height (or rather the line through the chassis mount and balljoint center) and angle the upper slightly down.
we can discuss your instant center now (and the corresponding roll center), but if you want to go fancy make upper control arm brakets to be able to slide them up and down to change roll center.
you also want to be able to change camber there and castor.
does that help?
dominik