More questions:
1. Was the engine in the same state of tune when it made 720-ish HP on your dyno as when it cranked out 750+ HP at the EMC?

2. Why the major "fat" dip in the A/F ratio down low? My first thought was that big-venturi "True 950" Holley wasn't happy under a load down there, but would have expected it to be lean, not uber-rich...

3. Do the flow #s you posted reflect the head being positioned in an "adjusted" location over the bore fixture comparable to where it was on the engine w/ the offset dowels, etc.?