Being an old codger, I prefer the look of stock...or maybe what appears "stock" to most, even though subtley improved ( in my opinion, any way).
My car has 15x8 Magnums in the rear with 255/60/15s, and 15x7" Magnums with 245/60/15s in the front.
I had custom-made rear leaf-springs made with a 2" height increase over stock, and the front coils are 1" LOWERING springs, but with a 1" aluminum spacer added to maintain stock ride height in the front...almost. The stiffer front coils plus the solid spacer actually increased front height by about 1/2".or so over stock. Plus, the stiffer springs help to keep the boat-anchor 429 from upsetting the front end as much when cornering. Nothing will make a big-block big-body Mustang what you would call a "handler", but this in addition to some nice KYBs and a bigger front sway bar helps a bunch.
The "rake" of the car is ever-so-slightly raised in back, which I prefer over the anemic stock stance with the rearend lower than the front. The actual factory- stock look always looked wrong to me.
Over all, the looks pretty stock to most casual observers unless another 71-73 is parked next to it.