Shane:
Remember that the 200lbs concentrated, or the 50lbs/ft. can act in either direction on the top of the wall. The top plate on that wall has to be connected in such a way that it will distribute these loads to 3 or 4 studs. I don’t know if you can stretch that as far as 84" though. That is obviously a nasty condition, and you must be able to get down into the floor framing to make some moment connection.
Why not treat the 42" high wall like a shear wall, torsion box, box beam, whatever; with plywood glued and nailed both sides. The exterior skin laps down over the full height of the rim joist, but the rim joist needs special connection attention too. The inner skin stops at the floor sheathing, but is nailed to the top and bot. plates, which might be 2-2x’s or 4x’s. Then, every 32" or 48" (fl. jst. spacing) use a double 2x stud spaced to allow a post tensioning rod btwn. these studs. This rod gets attached to the fl. jst. with some hardware similar to that shown in the mag. article for handrail posts, but in this case in a vert. orientation. This starts to provide the moment connection btwn. the wall box beam and the fl. framing system. I would consider an outward failure as the critical condition, so place the rod off center toward the inside of the wall. The outer skin acts as the tension tie on an inward failure. Don’t over tighten the post tensioning rods, they will just tend to loosen due to creep and shrinkage in the wood framing, but they are there to counteract any tension forces when loads are applied at the top of the wall. Maybe use the hardware on the fl. jst. and on the double stud, only a foot above the bot. pl. to minimize creep and shrinkage effects. There are also spring loaded take-up devices to account for this shrinkage.
