Ron,
Redline of Australia (
www.redlineauto.com.au) sells a Weber mainfold that incorporates a vacuum "box" cast into the manifold above the lifter valley. They leave it up to the end user to fabricate an aluminum plate to enclose the box on the bottom side of the manifold. A small hole is then drilled from the box to the backside of each runner, allowing each cylinder to contribute to the vacuum inside the box. You can run power brakes & the PCV valve from the box. A clever design. The manifold has 2V size ports but has enough material around the port to work with 4V heads as well. The mainfold uses adapters allowing it to mount either Weber 48 IDA or 48 IDF carbs.
Since Pantera owners usually opt for the "racier" 48 IDA carbs, you rarely read info about the 48 IDF models.The 48 IDF carb flows about 50 CFM less than the 48 IDA, but is a more streetable carburetor. The IDF carbs are shorter vertically & have off the shelf air filter assemblies available for them.
The 48 IDA carbs had gone out of production, but demand has been so high Weber chose to resume manufacturing them and importing them into the US. So they are available new again.
Dan Jones has much more data available regarding IR/Weber manifolds, including info regarding IR/Weber manifolds that a fellow Pantera owner is in the process of casting at this very time. Hopefully Dan will respond.
If you should decide to purchase the Redline manifold, I have an unused one, with linkage & 48 IDF adapters I'll sell you for a price you can't refuse, just to get it out of my garage. (48 IDA adapters are available from Redline)
George