If you want to run 3 degrees of camber on track but the track rod ends are not long enough you can use track rod ends from a Granada mk3, which are the same fitment but about 1.2 cm longer than the Sierra ones. As far as I'm aware the Granada mk3 track rod ends are also the same as the Sierra XR4x4 ones (also wider track).
Too much castor would only be a problem if the tyres touch the bumper. Not enough castor is indeed a problem.