Balancing the driveshaft should have been your First move.
The goal of setting the Pinion angle, is to have it equal and opposite to the front angle when under full power. Obviously then, cruising speed only requires about 35/40 hp, so the pinion angle will have to lowered. Furthermore, the spring "stiffness" is gonna play into this.
The net result of this is that I had to set my P-angle to 7* down relative to the driveshaft, even after adding one full-length extra mainspring on each side..
Your combo, I'm sure, will be different.
Anytime the the angle is not Zero, the U-joints are continuously speeding up and slowing down on every revolution at engine speed. At slower speeds you will feel this not as a vibration, but as a cyclical whu-whu that permeates the entire body and cabin. The faster you go, the more the whu-whu becomes a vibration. You cannot eliminate this. All you can do is mitigate it with isolation in the spring's bushings, and the transmission mount. Poly is very good at transmitting this type of vibration. The factory rubber bushings are pretty good at damping it. Bad shock-absorber bushings will also send it.
BTW;
a blown cord in a tire will also excite the body.