Turbine D
As you surely know, there are 2 more RWY´s at LAX, 24 L + 24 R. Both shorter than the southern pair and therefore not used, I assume. At least it wouldn´t make no sense at all to use a shorter runway if a longer one is available with these heavy departures.
RWY width of 200 ft. used to be the limit at the very early stage of introduction of A 3800, but a while later the limit was lowered to 150 ft. The much greater limiting factor to runway use are the dimensions and lay out of the attached taxiways. I know of several airports that had to widen taxiways or at least the shoulders. Also curving radii where a case of concern.
Ref. downwind take offs, I thought the general limit to that kind of operation is set at 5 kts.