Your GT5S A arms are the same as the 70's cars. You will need to make the top arm wider to get the castor you need. On the wide cars I have found 6 degrees of castor works well. I set the toe in a 1/8th and the camber at 1/2 degree negative (in at the top). On the rear I set the toe at zero and the camber at 1/4 degree negative.
Follow Jacks advice for bump steer on Pantera place.