If they moved the spindle/wheel centerline forward to center it in the fender opening when the clip was installed, you should have plenty of clearance for an HEI; if they set the clip so the wheel is in the original location, slightly to the rear in the wheelwell opening, it will probably be chancy, but you might get lucky; I think 3/4 to 1 inch is good, some guys have gotten by with a half inch clearance, it depends on how flexible you engine mounts are.