The Vehicle:
1987 Sammy recently acquired.
Brand New 31” AT’s
SOA
Pretty stock shocks
Old stock steering damper

The Issue:
The thing seems to arbitrarily want to change lanes for no apparent reason driving down flat smooth pavement. Not brake steer or bump steer, it has those as well, but this is different. I have checked and greased the front bearings; nothing seems outwardly really loose in the front end. I checked the toe, and it was a little toed out. I toed it in a little (what is the damn spec for toe anyway?). Not a lot of play in the steering box.

I have a new steering damper on order. Maybe the tie rod ends or something?

A few things I know can cause that type of situation:
A locking diff, can pitch you around while going down the road.
A loose or worn steering joint.
A wheel bearing, either front or rear going bad.
A loose wheel, check lug nuts.
Loose or broken leaf springs, and/or u-bolts.
Ghosts.

Too long front shackles fawking up the castor?

Since it is sprung over, I bet your caster is WAY off. Get an angle finder and park your junk on something level. Get under the front and put the finder front to rear on 2 of the lower kingpin bolts. You want your kingpins to angle BACK at the top, so if the needle is in front of the 90deg mark, you need to address this issue. If it is leaning back, anything up to 6 deg is fine anything more is way too much (I like 4deg). If it is the wrong way, you can use caster shims, shorter shackles, or a bit of both to correct it.
Travis..