416 running slower than expected

Hi everybody:
I think my combo is missing something because is slower than i may suposse, the most notorious at the big end, here's the list:
360 stroked to 416
4.060x 4.00
Flat top Icon pistons
Eddy ported heads and RPM Airgap
Holley Ultra HP 850
Custom Comp Cams mech flat tappet:
251-259@050, 570/594 lift, 106 lobe sep.
Timing 14° initial, 34° total
1 5/8 headers, X pipes and 3" cutouts
Mallory distributor and box, msd cables
Electric water pump
Ud aluminum pulleys
Tf 904 trans with trans pak
3800 Edge Racing converter
4.56 geared 9" rearend
28.5X 10.5 slicks
4 link suspension
60 fts is 1.68
1/4 mile 12:20 leaving on foot brake at 2600 rpm, shifting at 6500.
Any idea what may be wrong?
Think i can use bigger headers and a single plane (Edelbrock 2815)