Steering All Over the Place at 55mph+

If you are good at fabrication you can also rework the 67 K to take a 68/ later idler, but you damn near need a 68/ later for a pattern

So far as the wander, I'd get a pal and start from the top and work carefully down. Do not assume ANYTHING, and especially just because 'it was replaced.' Have a pal wiggle the play in the wheel while you look. Look everyplace there is a bolt, component, bearing, shaft, coupling, tie rod end, coupling or ball joint. Look for unwanted play and movement in everything that is supposed to move, and unwanted movement in everything that is NOT supposed to move. Bear in mind you might have a rusted/ weak/ cracked frame horn, K member, or the steering box loose on it's mounting bolts.

So far as alignment, you can do that yourself with very little special equipment.