[johnneilson]

The vibration, or sense of vibration can also be attributed to another factor.
The original flywheel was intended to assist in the inertia of the rotating assembly and provide low speed/rpm torque. Think about the roads and conditions back then, mud, snow, dirt roads for the most part unpaved. You needed low speed torque to pull out of many situations.

Now, the lighter flywheel will not absorb nearly as much of the combustion pulses/cycle of the motor. This will make the car/motor feel differently, especially if the modifications of the motor increase the efficiency and power output. You will feel more of the pulsation, after all, you have one combustion stroke per 180 degs crank rotation.

One last thing, the 8N clutch is not nearly enough clutch for a warmed up motor, the truck clutch has counter weights to assist in clamping for on the disk, 8N does not.

J