Rob, I don't think front end alignment can have anything to do with the rear track.

Look at it this way.......the front end alignment sets the tires with respect to each other and with respect to the body. Then the front tires go straight down the road. If the steering is not pulling in any one direction, we can safely assume that the tires are reasonably parallel to the direction of travel.

So, if the rear of the vehicle is tracking to one side of the front track, the only possiblity is a problem on the rear. My immediate thought is trailing arm bushings but, I recall that you changed these as well. If there is any play in those bushings, it will allow the rear to go all over the place. You'd feel this in the handling, however, if the track was that bad.

I'd do the wet pavement test.........maybe it's much ado about nothing.

If you solve it, maybe you can figure out why the '86 has developed a port side list.........by about 3/4" or so. Everything in the rear of that vehicle is brand new........as well.