Any ideas what would cause my '75 steering wheel to vibrate wildly when I go over bumps? The wheel itself has been changed and is a bit smaller than stock and seems to be a bit loose itself. I have not seen alot of wear on the wheels so I am thinking it could be the wheel itself is loose, maybe the gearbox. I dunno. Any thoughts?

Have you replaced the steering rack bushings and steering coupler yet? If not, this could be a lot of the problem.

Worn tie rods could be a culprit as well as the ball joints. Loose or worn wheel bearings could add to the problem too. If all these are in good condition the only thing left would be the steering rack itself.

I'd start at the rack bushings and steering coupler first, then on to tie rods ends and ball joints etc. Might as well start with the cheaper parts and then on to the more expensive items until you find the shaking is cured.