If the vibration is mainly in the steering wheel I would suspect tire balance. I have bridgestone Dueler H/Ts that vibrate the steering wheel at highway speed (after being balanced twice) and make a lovely wum-wum-wum sound at lower speeds, which is a characteristic of these crappy tires.

 

I solved my steering wheel vibrations with a "road-force balance". It needs to be done every 4,000 miles. The vibrations come back then I go get a road-force balance and the vibrations are gone. The road force balance can cost $100.

 

Have you checked for play in the tie rod on the drivers side near the steering rack? By one of your photos above, you have the old style rack guide which is notorious for excessive play. Do a search for rack guide replacement to see some threads discussing this issue further. This may not be your entire problem, but may be a contributing factor.

-Dan

 

I took a weekend trip which involved a good deal of highway driving and my problems seem to have disappeared almost completely. I suspect that the brakes were a little warped, and when I had them adjusted they were tightened down just enough that they made contact. I think my trip this weekend wore them in enough to stop that, everything seems back to normal. The new steering rack is super tight, and handles way better than before. Thanks everyone for the help, I have compiled everything useful into a guide that will hopefully reduce the need for threads like this.