As panic has indicated the whole point of the design is individual runners with balance tubes. The first pieces were called intake plates - built for SBC and later for BBC. The name is supposedly derived from Manifold Free Port Induction
There are some that hail from Conoga Park, CA. And other pieces were built in Atlanta, GA from a different casting(perhaps several iterations) (image from Steve's Nova Site)

Here's the CA design from Jalopy Journal

Mentioned here at Curbside Classics

Some info regarding Robert Patrick's patent on the design can be found here:
The Limited Monopoly Patrick hailed from Atlanta.