Rusty, what I meant was 21" or so runners give you the most HP, right? if the T/body is in the middle of the runners or on a plenum at the end do you get the same results?

This is sort of unknown.  If you had a slide type throttle, so there was no obstruction at all, I would assume that it would work fine.  The butterfly might, or might not cause a problem with the intake pulse timing. 

One thing is for sure, if you put your butterfly, and injectors that far away, throttle response will suck.  Been there, done that.  Mine were about 30 inches away though.  Throttle response was so bad as to be dangerous. 

Does this manifold adapt to a 6 port or 4 ports/

It's closer to 6 port, but it's not truly 6 port.  It's more like a BIG 4 port. 

Cheers,

Rusty