Guys, it's really 2 parts. MPH and ET.
Bad traction or a bad 60 ft will effect the ET, but not a hole lot on the mph. 3.23's with traction is plenty of gearing for a mild 360 with headers to get maybe 78-80 mph in the 1/8. In fact, without headers and 2.45's I got 78 mph in the 1/8. The real story is the OP got 68 mph, with 3.23's and headers, two things I didn't have. That is why I say the car should run at least 80 mph in the 1/8, which with tractions would equal at least mid 8's in the 1/8.
It's that simple.