Doug, when our booster went out in 'Vegas 12 years ago, I researched what was available and went with Bob Byars' GM booster/master cylinder assembly. Byars does quite a bit of work on the assembly to make it a true bolt-in for Panteras. His unit is a dual-diaphragm (separate diaphragms for front & for rear brakes), aluminum large bore master (front & rear are different diameters giving built-in proportioning; my totally non-stock brake system still needed a manual proportioning valve), rebuildable, built-in residual pressure valve for front, and it fit perfectly.
At the time, it was $100 cheaper than a stock Benditalia booster (still available in the Ferrari 308 series for $$$$). If one didn't know the car intimately, except for snap-on reservoir lids in place of screw-on lids you couldn't tell it wasn't OEM from the front trunk.
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.