Max certified ceiling for the -500 was indeed FL430. Have been there several times (at lighter weights of course) and no problems noted.
Yes, the Lockheed TriStar was the first wide-body aircraft with a super-critical wing section.
-500 series aircraft with the analogue a/p were limited to 506,000 pounds all up weight.
510,000 pounds for the digital.
No TriStar that I ever flew (and I flew 'em all except the -150/-250) had the outboard ailerons locked out with the flaps up...ie: it ain't a Boeing.
Of course, once it arrived on the UK register, anything could happen, and sometimes did.