Grizzly's instructions specifically tell you to snug the bolts, and
use a hammer to get all the seams right, then tighten the bolts a
little more, hammer a little more, etc.
Another trick I figured out: If the wings aren't coplanar with the
table (i.e. angled up or down), do this:
* Remove one wing, "fold" it over so that it is laying face down on
the table with the "seam" edges together.
* Line up the "seam" edges as best you can and clamp the wing down
* Use a file along the "seam" edges, keeping the file across both the
table edge and the wing edge, to make those edges coplanar. In my
case, I mostly needed to remove paint (yes, they painted the nicely
ground seam edges. Sigh).
* Replace the wing. Repeat for the other wing.
Even if the filing didn't give you a true 90 degree angle, it *will*
make the two angles you do get add up to 180 degrees - i.e, the wing
will now be coplanar with the table.
Note: this is the same trick as used on a jointer! Even if your
jointer fence isn't exactly 90 degrees, as long as the two edges are
jointed in the same direction (before flipping one piece over), the
errors will cancel out (if you do it wrong, the errors add together
and make it worse). Try and see - set your fence a little tilted,
joint to boards, and put them together.