I went by and talked to a distributor.
The wheels in this size are available with a ~6 day lead time.
Front: 18 x 8.5" $288 ea.
Rear: 20 x 10.5" $368 ea.
Not too bad actually. I didn't inquire about tires (I should have).
My current technical question is: The risk of the studs being long enough with the spacers... I would prefer not to get into a "stud replacement" project, that could be a lot of work...
My current aesthetic question (which I have to answer) is: How will these look on a Pantera with the ribs fully positioned on the outside of the tire? It's illustrated in Jan's picture, above. Based on a lot of the wheels used on our cars (and that I have grown used to), the wheel centers are inset into the tires, sometimes quite deeply. The TSW configuration is a bit different than I had in my mind.
I know there is a thread on wheel fitment pictures, I need to spend some tome browsing it, and see some similar examples. I went to the TSW site, but they don't have a Pantera in their library of cars....
Thanks again, George for pointing this option out.