I went with the MI SP on my low deck Ed head 496. It tested well on the Hot Rod manifold comparison and I wanted best possible air distribution for EFI. A dual plane should help lower end torque... but with 512 CI you probably have more than enough already. I figured a little help at the top end was more important.

It is super responsive at any RPM. It did require some tuning of the electronic "pump shot" to avoid stumble on acceleration below 2000 RPM. It will now accelerate smoothly from 1200 RPM in overdrive if that is what I want.

I recently pulled it for freshen (pic). I'll post dyno results shortly. With >600 ft lb torque at 3000 RPM it does keep up with traffic OK...