I think the 4500 Barton manifold would run better on your combo. I'm assuming they make one w/ the correct bolt arrangement to fit your heads?
When I tested the Barton and the big -4 Indy on my car, the difference down low was surprising. The Indy -4 screamed up top, but was almost a full tenth slower to the 60'. With a looser converter and the ability to turn more RPM, it would run well NA. My combo just isn't suited for high RPM.
The only reason I currently have the big -4 on my car is b/c of the nitrous.

The smaller 426-3 matches the Barton's lowend power, but is really lacking up top. The only reason to use the 426-3 is if you have hood clearance issues b/c it is a good bit shorter.
The Barton is way heavier, but it makes up for it.

Overall height...............Weight.
Barton...7 & 9/16" .........35 lbs
Indy 426-3...6.5"............19 lbs plus 3 lbs for the valley plate
Indy 426-4...8.25"...........22 lbs plus 3 lbs for the valley plate

Pic is the Barton on the left, the Indy 426-4 on the right