A 1/2 inch spacer is pretty extreme. A 1/4 to 1/8 spacer is OK , but beyound that, you'll have to put in longer wheel lugs. you can get your old ones out by taking the bearing spool off and driving the lug out the back, either by press or hammer and drift. Most Autoparts stores should have an assortment to match up a longer lug (stud) for you. You want No less, I mean NO LESS than 5/8ths inch of full thread engagement. If the threads in your lug nut don't start for a 1/8th or 3/16ths of an inch, be aware of that and add that extra length in. So look to have about 3/4 inch of lug showing with the wheel in place.
Tom Kubler, Long-time Mustang Enthusiast & San Antonio Mustang Club Founder