Which intake manifold

A single plane with long runners will have more benefits than any dual plane for your 541, you're not going to miss out on any torque, if it were less, it wouldn't be noticable on your butt. You're rpm range will be better, torque carried into higher rpm equals more HP.
Oh and I think that 700 hp mark is going to be off by 50 or more HP, based on Andy f & his 470 with 240 heads, I think his 512 with 270s was over 800