The indy dual plane if you have a good (non core-shifted casting is an excellent 500" manifold, it needs a little lower plenum transition porting to the runners but flows VERY well.

I also like a well-ported Holley Street Dominator for that combo, easier to port than the M1 (which has tall/narrow runners) on a 500", I had one on my old 508" RB with ported Stage V heads that had an ~3.25 sq Inch port cross section which is about the ideal balance of maintaining great velocity and still giving you sufficient flow and power above 5500 rpm with the 500 inches.

The only other real drawback to the M1 single (other than it's rather "bland" to look at under the hood) is it's pretty tall for a stock hooded B or E body.

Yes. I remember picking out the Indy dp and the Mopar Nationals years ago at the Indy tent. They had 3 or 4 to choose from at the show, I picked the one with the least amount core shift