Random but violent front end vibration

Good suggestions so far...

May be a silly question, but you do have large ball joint upper control arms on there with those 73+ disk brakes yeah? Or tapered adaptors to go small ball joint UCA to large ball joint taper in the spindles?

Beyond that, alignment - marginal toe in or negative caster would be things to look out for. Then worn out parts, especially the pitman, idler, tie rod ends, ball joints, etc. And then there's always cracked welds, it's not uncommon at all for the LCA pivot tubes to break loose in the K-frame, or the steering box mount welds to fracture entirely leaving the steering box loose.

And since we're checking things- did the steering wheel shake? Or just the dash? You may also want to check over the u-joints, driveshaft, rear end etc, because if the dash shook but not the steering wheel there's a chance it might not be front end stuff.