Will, did you check your front bushings yet?... I'm in the middle of buying a new house so I haven't even put much thought into the problem recently but that's the first thing I'm going to check. My tires are old and very hard so I'm hoping that's the problem but something tells me it's not. The closest I can describe it is that it feels like the wheels almost fold under the car slightly on hard left or right turns.

Since the wheel bearings are good, the steering is good, the car tracks straight in a straight line, I'd guess worn tie rods or ball joints.

If the car has been lowered have you thought about the ol bump steer kit?

Update-

The car has not been lowered and is at factory specs.

Another update....
New tires fixed this problem for me...and the car rides a 1000 times smoother.

my 77 acts the same with the track tires on the front. (MPSC 225/50x16 on 16x8 Fuchs- 911 offset)
the problem goes away when I put the street tires back on (Kumho ESTA 205/50x16 on 16x7 Fuchs)
I think it has to do with the size of the contact patch, stiffness of the sidewall, and the age of the components.

Bill K