Bill, I happen to be in the 'modify it if it doesn't function as you'd like' school. The function of wheels too wide to fit the original body is to enhance/improve high-speed cornering beyond what proper tires on 8" wide/10" wide wheels can provide. The function of the wing is to stabilize the rear end at speeds in excess of 150 mph (according to one test done in England where lap times were reduced WITH the wing mounted). So if you don't mind the expense of the wider tires and driving like this is how you envision your use of the machine, fine.
The wing, surprisingly to me- IS functional at speed and apparently does not add very much aero drag. It also works as a stand-up picnic table during outdoor car shows and is strong enough to act as a seat for several reasonably-sized young women. Giant tires do add measurable drag.
Flares to cover wider wheels/tires can be steel or fiberglas and can be in GR-4 or GT-5 styles, which are noticeably different. The value of a modified Pantera is in the eye of the beholder and is likely a function of the quality of the bodywork and the preferences of a potential buyer. But currently, even a very well done all-steel modified car will not approach the price asked for a original GT-5, regardless of the quality of the work. IMHO, anyone that buys a Pantera primarily for its investment qualities rather than the thrill of driving it, deserves whatever happens.