I have no specific knowledge in off the shelf header fitment. I went with Hall Big Bores for my first engine. However, I wouldn't even try it unless you can get someone to verify they fit a Pantera unless you have spare pipe and welding experience. I would suggest looking at the Pantera vendors offerings. Wilkinson has a very nice setup for the entire exhaust system. Personally I love the sound of 180 degree header systems. Good luck and welcome to the Pantera community.
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.