The purpose of dual-plane intakes is to give better vacuum signal to the carb and separate the cylinders that fire right after each other on the same bank for better fuel distribution. Totally pointless with port EFI, that's why all modern engines run "single plane" intakes with long curvy runners and GIGANTIC plenums (the old 5.0L HO Mustang engines are a good visual example, or a modern Gen 3 Hemi). Most of the bottom-end torque loss you get with a single-plane manifold and carburetor is due to the poor fuel distribution and weak/unsteady vacuum signal at the carb; EFI brings most of that back.
I haven't measured it myself but it seems like the difference in runner length between a carb'd single and dual-plane is only a couple inches anyway...? I don't think that alone will affect the torque curve much.
