It is more efficient to run with a 4 bbl then a 2 bbl carb. With a 2bbl the 2 barrels of the carb have to be sized large enough to run at WOT, which means lost low RPM grunt and poor economy at lower speeds. With a 4 bbl the 2 primary butterflys are typically smaller then the butterflies in a 2bbl carb which means better low end response and better economy. Under WOT conditions the secondaries open after the primaries which inturn helps make more top end power then the 2 bbl.
As for the intake manifold, I have made intake manifolds for inline engines from tubing and have seen dragsters with inline engines running handmade manifolds that seemingly work fine.