A set of 3.91 or 4.10 gears would wake thar car up!!!

Next thing would be a 10" torque convertor if it is an automatic.

Get a Thermoquad off a BB from the wreckers and rebuild it yourself.

After that it gets expensive,,,

Good luck,

Arnie

67 Cuda 8.48@ 158.7 mph 1.18 60' 2,600 DA(so far...) 70 Super Bee 440 Six Pack 4-speed. 13.2 @ 104 Stock exhaust/Street tires.