I think a set of shorty headers with unequal length tubes (for ease of install) would be a BIG hit. Think about it. People pay $450 for 37 year old cast iron manifolds because they want an easy install more than they want absolute maximum power.
Ford, BBK and others have sold about a jillion of the things for 5.0 Mustangs, and Mustangs are infinitely easier to install headers on than an A-body.
They'd make significantly more power than manifolds, without all the hassle of longtubes.
Ball and socket collector FTW.
Steve