You can get a performance cam for a SD setup, it just needs proper lobe timing to maintain vacuum sufficient for MAP readings. The bigger problem is that while you can choose any cam you want (basically), nearly any cam you choose will require a professional tune unless you swap over to MAF, or unless you get a SD specific cam.
you'll want to get a Mass Air Flow, a speed density system uses fixed air/fuel curves so if you do anything to take it away from stock airflow (i.e camshaft) it'll be totally lost. A mass air flow meter will learn on the fly and adjust your air/fuel mixture accordingly.
Check this article out: http://www.musclemustangfastfords.co...n/viewall.html