There was a post by George Pence back in January, 2012 (for which I made a hard copy, but cannot readily find at the moment)which stated the original Pantera diameter was about 25" front and 26.8 rear and went on to suggest 245/40/17 front and 285/40/17 rear.
I have been looking in www.tirerack.com to look for matching tread patterns, wheel width specs, overall diameter (for speedometer consideration)and sidewall profiles.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.