i was looking threw Griggs racing and found this
Mustang Front Fender Modification Installation Instructions
Due to wheelbase and track increases* built into the GR-40 suspension kit, it may be necessary to modify the plastic liner fender liner and body side molding extension at the lower leading edge of your wheel openings. For best results, follow these steps carefully;
1. After final wheel alignment and ride height adjustments trim away plastic inner fender liner from frame rail to outer fender lip using a utility knife or razor blade. Begin each cut at the frame rail taking care to remove material from in front of the plastic press-in retainers that attach the liner to the frame rail.
2. Remove front fender support bracket which runs from the upper radiator core support to the inner fender flange (where front bumper cover and fender bolt together). This bracket, and the flange itself, determines the shape and width of the lower edge of the fender.
3. Using a cut-off wheel or tin snips cut a 1/8 inch slit in the front fender flange, all the way to the outer surface of the fender (about an inch on most cars) immediately above the body side molding. This will allow you to flex the lower portion of the fender into virtually any shape. The end result will be a flared lower air dam and fender that looks very much like the nose of a Trans-Am Mustang. The entire leading edge of the tire will be behind the air dam, permitting enough tire clearance for 275/40/17 tires on some cars.
4. Proceed with normal rolling of the inner fender lip, taking car not to damage the exterior paint.
* The track and wheelbase increases improve the stability and handling of the Mustang.
Mustang Front Fender Modification Installation Instructions
Due to wheelbase and track increases* built into the GR-40 suspension kit, it may be necessary to modify the plastic liner fender liner and body side molding extension at the lower leading edge of your wheel openings. For best results, follow these steps carefully;
1. After final wheel alignment and ride height adjustments trim away plastic inner fender liner from frame rail to outer fender lip using a utility knife or razor blade. Begin each cut at the frame rail taking care to remove material from in front of the plastic press-in retainers that attach the liner to the frame rail.
2. Remove front fender support bracket which runs from the upper radiator core support to the inner fender flange (where front bumper cover and fender bolt together). This bracket, and the flange itself, determines the shape and width of the lower edge of the fender.
3. Using a cut-off wheel or tin snips cut a 1/8 inch slit in the front fender flange, all the way to the outer surface of the fender (about an inch on most cars) immediately above the body side molding. This will allow you to flex the lower portion of the fender into virtually any shape. The end result will be a flared lower air dam and fender that looks very much like the nose of a Trans-Am Mustang. The entire leading edge of the tire will be behind the air dam, permitting enough tire clearance for 275/40/17 tires on some cars.
4. Proceed with normal rolling of the inner fender lip, taking car not to damage the exterior paint.
* The track and wheelbase increases improve the stability and handling of the Mustang.