These are the best fit now for the rear. Mickey Thompson 26-12-15. Built for an 8-10 inch rim.
The BFG 295-50-15 is also a good fit and easy to get. It only has an S rating though. You can get the bigger tire in, the 305 Euro T/A but they were discontinued a while ago.
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.