Brake Booster Question

Start with checking the tires for slipped or broken cords, or out-of-round; and balance of course.
Then the toe-in.
Then the u-joints.
And finally the pinion angle.

If it was my car, I would go straight to the pinion angle, because
I know my tires are ok, and so on.
The pinion angle has to be "nose-down" relative to the driveshaft, and stay nose down under power. A broken rear spring, or saggy springs, cannot control that with a hi-torque engine, especially with an altered ride-height.
Your car looks a lil low in the back, and that steals caster, which de-stabilizes the front end. So if there is a condition there that already wants to vibrate, the lack of caster will allow it.