Haven't read every single post, but so far haven't seen anyone mention checking the pivot blocks aren't twisted.
I put the chassis on flat surface, with removed top deck.
Gently tap each corner of the chassis with one of your hex drivers, pretty close to where the droop screws are. If the chassis is flat, tapping it will make a 'dead' sound, if that corner is bent up at all it makes a much thinner 'tapping' sound (this sound seems a little more obvious if performed on a glass surface, but again, must be dead flat)
In extreme cases you can even see the chassis move down when tapped.
If you get a difference in sound, or get the movement.
Go underneath and loosen the bulkheads at that end, then try again.
If you still get it then try loosening the pivot block mounts and see if it goes away.
This is a process of elimination.
The most common bent alu part I get is the FR block (Xray) as this takes most of the strain during any sort of front crash.
If you think a particular block is bent, remove it and lay it on the flat surface and perform the 'tap' test on each end, rotate the block 90deg and repeat. Again, if the part is bent you'll see it rock slightly as well as seeing a gap under it at one end.