Brett,
Are you running an OEM '78 Mustang II front end or aftermarket? If OEM then they should be able to plug in a '78 Mustang and be OK. If aftermarket hardware you should probably check with the manufacturer to see if he has anything special in his caster values. Barring that the basics for a Mustang II front end are in the order of 1/2 degree camber on the left, 1/8 degree on the right, 1 1/4 degree caster on the left, 1 1/2 degree on the right, and zero toe with radial tires unless you are getting bump steer. A good front end guy should be able to set you up if you just tell him what you have in hardware.