[cycleguy55]

From Jim Inglese's website:

Supplying vacuum for transmission, air conditioning, power brakes, or PCV

Some cars require vacuum for accessories or to connect a PCV hose.

The 8-port vacuum kits are generally hidden on all the downdraft units, and all you'll see are fittings at the rear of the manifold as shown here. Vacuum is supplied from all eight ports.

The one at left has two 3/8" nipples, one for PCV, and the other for power brakes.

If you require vacuum, please be sure to order this option (cost is $175) when you place your order. It is much more difficult to install once the unit is assembled. In some cases, it CANNOT be installed later, because not every manifold is designed for hidden vacuum. The right manifold must be ordered in the beginning.

https://www.jiminglese.com/8-stack-v8-systems