HZ has 3 x different tyres. The one Robbo mentioned is option QEU (the XX7 tyre). XU3 used QCP which had 2 x different specs. Post 6/9/77 they were FR78S14 4 P/R steel belted tubeless radials, and before that I have yet to find the right paperwork, all I know is the spec changed. Possibly the early examples used non steel belted radials?