"Refacing" cams is called hard-welding them. And if you use a hard weld cam, you must also hard weld the rocker faces. This gets expensive quickly. But, for a performance build its almost necessary.
For your situation, CB750 gave you great advice. Find a good quality 650 cam and stuff it in and go. You also need to change the tach gear and tach gauge to a 650/750 unit as the ratios differ. Or find a good condition stock 550 used and plop it in.