[JBo]

Rear uprights from a 428 frua widen rear track by 4 inches, filling wheel wells a bit better.
Center mounted fuel filler ala 289's and Aces, fuel tank in scuttle rather than under car.
FRG inner fenders, foot rest for drivers left foot in footwell (running change-exists on 1113), asbestos ( or something) attempt at controlling cabin heat in engine comparment and under passenger area. I'm sure there are more...but the MKIV was basically a 289 sports with crash bumbers and doorbeams or a modified MKIII if you you will.