Due to the limited sizes of tires that are currently available, I am taking a poll on what size rims are the stock bodied Pantera's running other than the stock 15"?
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17" x 9.0" and 18" x 12"
There are at least three matched sets of street tires available to suit these sizes of wheels (BFG Rival S 1.5 (new), Pirelli P-Zero, Nitto NT01*).
*=note: these are officially D.O.T. rated competition tires but according to numerous sources, including Singer (the "cost-no-object" Porsche 911 builder), they are great street tires for people who don't normally drive their cars in the rain. Same compound as the Toyo R888 but with a more streetable tread design. Available in 235/40-ZR17 front and 305/35-ZR18 or 335/30-ZR18 rear. If using a 305/35-ZR18, you may want to use an 18" x 11" rear wheel although 18" x 12" is an approved width.
18” X 9” & 19" X 11"
245/35/18 & 325/30/19
Frank, you may find this table helpful down the road.
My Pantera had this set when I purchased it:
245/40ZR17 mounted on 17x9 (25mm offset)
315/35ZR17 mounted on 17x11 (12mm offset)
I wanted to experiment with wheels that were 2 inches different in diameter front to back, so I installed this set a decade ago:
245/35ZR18 mounted on 18x9 (25mm offset)
325/25ZR20 mounted on 20x12 (12mm offset)
I really like the appearance of the 2" stagger in wheel diameters of the second set. Laslo Antal is the guy who got me interested in trying that out. That's his car you see tiled in the background of the forum pages. His car had 16" front tires and 18" rear tires. I could have chosen 17" front and 19" rear, but I took things a bit further. 
Down the rabbit hole.
I'm planning another change in wheels, so I'd like to share where I am at in regards to wheels and tires. With the hope that in discussing my "journey" it will provide all who take a moment to read this with food for thought.
After installing the 18"/20" wheel set I became aware of other aspects regarding making the tire and wheel package look better, there are things I would do differently "next time"; i.e. narrower wheel widths to square-up the sidewalls; and less offset up front, more in the rear, to recess both front and rear tires an equal amount. Those things are reflected in the table above.
I think the expectations for wheel and tire fitment were much lower in 1971, but today the expectations are much higher … at least mine are. Today we expect wheels and tires to fit within the fender arches like this ↓ .
I came to the conclusion that the ultra-wide rear tires are for show cars and for folks who "just need" the wide tires. I'm not criticizing anyone's choice, after all I was among the folks who "just needed" ultra-wide rear tires, but I've come to the realization that a narrower rear tire (i.e. a tire in the range of 275mm to 295mm) is more appropriate (more practical) for many applications including mine. If you think about it, its kinda odd referring to a tire that is over 10 inches wide (275mm = 10.8 inches) as a "narrow tire". They really aren't narrow, they just aren't as wide as the "ultra-wide" tires. The narrower tires will allow the rear tire to be recessed within the wheel house to match the front tire whereas the ultra-wide tires must be mounted flush. That discrepancy bugged me with the last two sets of tires.
I wouldn't change the 245mm front tire however. The effort during parking maneuvers is a little high but tolerable. Once rolling the effort is perfect. The tires rubbed a little bit inside the wheel house at full lock (i.e. parking maneuvers); with less offset there would be no rubbing at all.
De Tomaso's last sports car, the Guara, had 245mm front tires and 285mm rear tires on 18 inch wheels. This was a cutting edge tire set when the Guara was introduced in 1993 (26 years ago), it has become a very common tire set for sports car since then.
I mentioned that I'm planning another change in wheels. That's because I would like for my Pantera to have OEM looking Campy wheels, but like Frank I really don't like the 15 inch tire scene. However Roin Technology is working on an 18 inch version of their Campy replica wheel. IF Roin develops an 18 inch Campy replica then there SHALL be another wheel and tire set in my life. That next set of wheels and tires shall be:
245/40ZR17 mounted on 17x8.5 (16mm offset)
275/40ZR18 mounted on 18x9.5 (8mm offset)
That is a more moderate tire set than I consider ideal; i.e. smaller diameter wheels and thus taller sidewalls. But to use Roin wheels I have to compromise a bit and choose tires that remain within the wheel diameters Roin offers. I don't feel there are any good options in 17 inch rear tires; i.e. the selection of tires is limited, and the tires that are available are too small in diameter. So I'm waiting for the Roin 18 inch wheels to become a reality. I consider this the most moderate tire set I would consider installing today in 2019. If I didn't constrain myself to Roin wheels, I'd opt for 18" front wheels (245mm tires) and 19" or 20" rear wheels (285mm or 295mm tires).
I'm OK with the 1/2 inch taller sidewalls because they shall protect the wheels from damage (pot holes) better and provide a slightly more compliant ride. In other words they have practical aspects that redeem their use. I chose the 275mm rear tire because combined with the 245/40ZR17 front tire it has 18 tire sets available on Tire Rack, one of the highest set counts. Set counts for any of the possible front tires with a 285/40ZR18 rear tire are 3 or less. Front and rear tires are almost 2 inches different in diameter (1.95 inches to be exact) which is what the Pantera chassis and fender openings dictate. Front and rear tires both have an aspect ratio of 40, and the difference in side wall height is only 1/2 inch, the difference is minimized by the one inch difference in wheel diameter. This is all good engineering.
That's where I'm at in my journey in regards to tires and wheels. You can see more pictures of the first two tire sets on my Pantera's photo page, the link is in my signature line (signature lines can only be seen if you're logged-in). Sorry for my prolixity.
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My Wheels are 17X8 and 18X11 (73 stock body) the Tires are Continentals Extreme Contact DW 245/40/17 and 295/35/18. I'm the first to say I like the Steam Roller look on the back, but that comes with a Price! The few 335s out there are costly being about $450 up per tire. Ouch! In 2014 my four tires were under $1000.
I have similar sized wheels and planned on a 245/40-17 front and 285/40-18 also in the Extreme Contact Sport. Hopefully they keep producing these sizes.