Dart 1969 - faster 1/4mile

Actually just using the calc for yours, 560hp@3200lbs? 4.88/31"tyre....shows this>
60 Foot E.T. : 1.45
1/8 Mile E.T. : 6.57
1/8 Mile Trap Speed : 103.45
1/4 Mile E.T. : 10.41
1/4 Mile Trap Speed : 129
1/4 Mile Trap RPM : 6,811+ on average 8% slip? = 7355rpm
a gear change down to 4.30 would drop that to 6500@traps, with 4.56/6900rpm.