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 InductionThere 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.