well... im goin from memory here, so i might not be 100% correct. as i recall he moved the frame rails inboard at about the wheel houses, then proceeded to do a "standard" mini tub on the wheel wells(cut and add)
this is a major undertaking, not for the faint of heart, i would almost suggest finding and alternate way of stuffing the tire in the room available. carefull backspace measurements, and possibly buldging the qtrs out a lil(64's are curved everywhere anyway, a compitent body guy should be able to "handle" it without it being noticable...been there done that
)
the last 64 i did was way low with 275 40 17 on an 8.5" wheel...dont remember the backspace.... the lower shock mount needed a lil rework to clear the wheel also(that might have been another car...i dont remember). the car also had the narrower rear, as i recall it made it a PITA finding the right offset.
hope this helps