The indy dual plane is a Max wedge manifold with big MW plenum chambers but (as delivered) the runners are tapered down to 440 size ports, they are very easy to open up if you go max wedge and will support a 700+ HP motor.

The SD used to be my favorite 440 street/strip manifold and it is a great "default" 500" stroker manifold in cases where a dual plane could give you more torque than you can put to the ground. But the 440 2-D is now because it's the most versitile and will produce broader and higher average torque up to ~700 hp than any single plane with an Automatic and moderate street gears/stall. The Performer RPM is a great piece but it is more limited internally in terms of how much you can port it, the 2-D does everything an RPM can do and has potential (room to grow) to do more.

Allegedly the 2D is based on the 426 Max Wedge NASCAR intake, In well-ported form it pulls up past 6800 on a 12:1 517" low deck motor with some of the very best flowing MW heads out there, Chapman Stage VI maxies.