ok, lets reason this out. if the wheel brgs. were loose, the brake disc would be hitting the disc shield because it is attached to the vertical link, not the disc. therefore, the vertical link is moving and the pivot point for this movement would be the trunion. if my reasoning holds up, then the problem is either slop in the top ball joint, loose ball joint mount to the upper a-arm, or the upper a-arm bushings are worn. if the problem was a loose fit of the vertical link in the trunion, that connection would have be so loose that that the vertical link would likely pull out of the trunion.
or it might be a loose stub axle. would love to know the answer.
just my thoughts because the last time i worked on a triumph, they were new enough that they didn't have these problems (1968).