I ended up going with the booster/master kit from http://precisionproformance.com they have a upgraded GM booster, but to finish this post off for anyone who might need the stock part number My Master Parts Catalog shows it as a "28195 Booster Assembly". The stock Pantera brake booster was a Bendix-Italia unit (Benditalia) also used in various '80 & up Ferrari 308 series. Info from Jack DeRyke, and Jim Nowlin.
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.