Check the shop's diagnosis. With wheels on the ground, have your friend turn the steering wheel slightly back and forth. Look and feel for any play in the steering linkage and tire rod ends. Then, jack the front up and support it on the frame rails, w/ tires on for safety. Try forcing the tires back and forth, looking for play in the ball joints and control arms. Measure the toe-in w/ a tape measure (front tires: aft track width - fwd track width).

In my limited experience, worn lower ball joints don't cause vibrations while driving. One of my 300D's had one so worn that the ball could almost pull out of the socket, yet it drove fine. Similar for worn rubber control arm bushings, though they will give clunks over railroad tracks. My guess would be something in the upper control arms, like a broken sway bar end or bad rubber bushings on it (secures upper spindle) or excessive tow-out (causes car to wander). These cars also have complicated independent rear suspensions (requires alignment), though I haven't read of wear there causing such vibrations. I never touched my IRS parts.

Please let us know what you find.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans