Ok, I got it.
Problem # 1: aluminium bracket top bezel (holds screen in place). This locks into a channel formed between mirror frame and top plastic chassis. It's rear dimension (the short edge that locks in) is too tall by about 1-2 mm. This "spreads" the chassis/mirror apart putting pressure on the mirror brace bending/flexing the mirror out of shape. File (or dremmel) between 1-2 mm, then bend the bracket to about 1/2" deflection (up in the middle). Before bending the bracket test fit onto the chassis, you want a tiny bit of up/down play when it's attached: when assembled it will now support the plastic chassis without putting pressure on the aluminium mirror frame. The mirror and chassis are attached: Bending too far will have the opposite effect turning the smile shaped bowing upside-down.
Problem #2: Bottom bezel misshapen/bowed out. I think this might be by design to give the lower bezel a rounded appearance in relation to the bottom "foot" which is circular. It exacerbates the effect of #1 above. At the 4 screw points that attach the lower bezel to the chassis (the 4 upper screws), on the front of the chassis there is a "standoff" built into the chassis (protrusions that look like an "="). File those off. Also file about half of the long thin horizontal standoff that runs between the two middle screws. Now... when assembling the screen back onto the chassis DO NOT screw these tight! Consider them a screen adjustment. The right 3 (at least on the 56") can be reached with the TV operating with long or stubby phillips drivers. Tighten the two middle screws only enough to remove any bowing left after correction of problem #1. Remove guts, then tighten outer two screws until they seat against the chassis + 1/8 turn. If you use the TV speakers these may vibrate/loosen. Use teflon tape or threadlocker to keep them set.
Potential problem 2.5: check 4 quick release/alignment posts (bottom set 4 lower bezel screws) are properly seated. They should rotate (like a radio knob) about 1/4 turn. If they dont, they arent assembled properly and will space the lower bezel out making adjustment #2 impossible.
What I can't believe is that these sets got past the prototype stage with these "simple dimensional correction" issues present. Once I ruled out the light engine and looked at the chassis, it took me less than 1 day to determine the nature of the problem brainstorm up a correction. Samsung would have a "team" of design engineers paid to figure this stuff out, so why didn't they? That top bezel bracket really should be steel (as well as "resized").
Someday when I'm somewhere else (not behind this firewall of armegeddon) I will post a pic of my screen with the small hatch pattern pulled up with it's (now) beautiful near perfect geometry. I acquired it unwatchable...have seen other post pics similar, with bottom OSD smile shaped and cut off ("Enter") not visible.