Using the search feature and the words "66 wheel well" I turned up the following
http://www.concoursmustang.com/forum/index.php?topic=16170.msg101228#msg101228Seems you had a similar request in 2016
http://www.concoursmustang.com/forum/index.php?topic=14932.msg93056#msg93056http://www.concoursmustang.com/forum/index.php?topic=12126.msg73529#msg73529Should only find very little red oxide in a wheel well - typically. Sound deadener would have been applied over it (except for the the very outer edge above and behind the wheel well lip shadow plus a little extra)) as the rest of the visible surface would have received a nice coat of body color a the spray gun applied paint to the wheel well lip and passed over the wheel well opening multiple times.
Sound deadener was applied from below so it could be found in so different pockets where the body color would not have been directed though some overspray may have traveled there as a mist
In the upper surfaces of this wheel well time and use has worn away some of the body color plus its a bit dirty also
In the picture (though contrast to a red oxide with this exterior color is not great) you can see body color on the gas tank panel drop surfaces facing outward
Sound deadener on the frame rail and the thin section of floor (out of view) would have little to no paint since the wheel well lip would have produced a shadow
As mentioned in the undercarriage article typically you would have the blow out from the pinch weld black out at the forward and rearward areas also though not visible in this picture