Relocating inner wheel arches

In an effort to fit wider tires under a 65-70 Mustang this modification is a relatively simple method that won't change the body lines like flares would.  The car pictured below is a 66 coupe.  This car runs no back seat or interior trim.  Careful consideration should be given if you wish to re-install the interior trim and back seat.  These directions are in no way meant to be a definitive guide, its just how we did it.  Your car, skill level and desired end result may dictate a different method.

This modification is really only beneficial if using our 3-Link with frame rail mounted trailing arm brackets so the leaf springs are removed and not in the way.

First step would be to clean away any undercoating back to metal so you can see the seam where the inner and outer wheel arches meet.  We then made a cut with an air saw approx. 1/2" in from the seam of the inner and outer wheel arch, all the way round and up alongside the lip in the frame rail:

You are then able to remove the inner wheel arch:

Our 3-Link uses bump rubbers mounted on the shock shaft so the stock bump stop is no longer needed:

We then cut off the frame rail flange and the remaining overhanging trunk floor.  Using a thin cut off wheel for the straight cuts and our air saw for the curved ends:

Then grind the remaining overhang flush to the frame rail.  This gives the inner arch a nice flat surface to sit against:

Now over to the removed inner wheel arch.  The remaining trunk floor can be trimmed from the interior side of the wheel arch as well as the overhanging trunk floor flange:

We then used a knotted wire wheel to clean any seam sealer from the joint.  Then, a hammer and dolly to flatten the 2 pieces of metal ready for welding to the frame rail:

With the inner arch back up into the chassis, align the 2 halves and tack into place.  Check fitment then weld the edge of the inner arch to the frame rail:

A quick measurement shows we've gained 3" in the front and 1.5" in the back:

Our 245 Hoosier now has plenty of room.  Looks like wider rims and tires are in our future!

Filled the gap with some 16ga stock:

You will also need to trim and relocate the trunk hinge brackets:

Covered the seams with seam sealer:

Painted: