Posting it up for you bud.

660HP from a mild 540, at 5600RPM, is excellent numbers. The torque curve and peak point, is also excellent. Very nice combo. My guess is it has a very mild camshaft in it

I have to ask though, was this particular pull, where the engine made its best numbers? If the AFR data is correct, my gut tells me you may have been leaving a little power on the table being that lean.

On big block's and based on some of the input single plane seems to be a obvious choice on small block's id be hard pressed to agree with that. Actually could it be due to lack of proper intake design for high HP big block's? Even on small block's there increasing the plenum size to accomidate higher power aka more mass or air. The vid's a bit corny but it does address the issue.

http://www.youtube.com/watch?v=i2DvnoHWagk&feature=player_detailpage

I think your on to something!
I think Mild said it best when he suggested a better set of heads, just the intake is not going to do much!

I'll tell you my thought about that A/F ratio.

I'll bet a $100 the A/F ratio was derived from the airflow meters #'s vs the Fuel Flow Meter #'s. Not a wideband.

If that was a wideband, why was the engine not tuned while on the dyno ?

It is not a super accurate # and no real info can be attained from it. Not uncommon to be a point higher than what they should be.

In me experience the fuel flow meters are more accurate than the airflow meters. I look at both #'s seperate for other things but never together for a/f ratio.

Those were the best numbers and I've been told by someone else that it's dangerously lean. Your thoughts? Also, that run is with the addition of a 2 inch spacer which made a big improvement across the board. So single planes don't necessarily hurt mid range. Just sent you a pic of the chart prior to the adding the spacer.