I like the painted covers better...looks nice!

How much room do you need for an air cleaner? FWIW, I can't fit an air cleaner on mine now either w/ the Indy 426-4 manifold and a 5" cowl.
The Indy 426-3 will hurt power substantially.
The Barton is your next best single 4500, but it may not give you enough clearance. It's roughly 11/16" shorter when measured sitting flat on a table.
Barton is 7 and 9/16" tall, Indy 426-4 is 8.25". The Barton manifold is 10 lbs. heavier too. shock

If you decide to go w/ two carbs, I'd use the Stage V manifold.

CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax