Ok, I forgot you already had the heads and Hughes did the port work. Yes, 560 is good power.
My 408 had Edelbrocks ported by Curtis Boggs, was a 10.9-1 pump gas street/strip deal and had a Hughes flat solid cam. It ran 6.57 with 1.38 60' at #3260 on radials. It was never dynoed but would guess it was close to your number.
Is there a reason you dynoed with mixed gas? My last three small blocks have all had aluminum heads and were 11.4-1, 10.9-1 and 11.2-1 and ran great on pump 93. The 434 in my Dart now is 11.2-1. When I dynoed it we started and tuned it using 98 leaded race gas. After tuning the carb and timing we drained the carb and pumped the cell out and filled it with pump 93. It made 30 more hp and 24 foot pounds of torque with no other changes. I didn't believe it was right so we cooled it off and made another pull with the same results.