It took three weekends but now finally, the wing jig is completed.
In this last stage of construction, I attached aluminum angle attach horns to the 4x4 wood posts.
On the outboard side, I attached a fixed angle that will hold the W712R rib just under the spar with 2 AN3 bolts. It is sufficient on this side to have the bolt (and thus the hole spar) level on both vertical and horizontal side.
Then I attached the inboard side of the spar to the other posts with a horizontal alu angle which is supported with a 45° angle piece of angle. I made an opening in the angles so that I can still adjust the position later on by just loosening, positioning and tightning again.
This is the idea of what you should finally get when you will start levelling the spar in the jig : 
I will make a close up picture and post it here soon of the inboard side attach angles.
Below are some pictures of both spars levelled in the jig.
The measurements along the spar are now level but this is not precisely true. The spar has some sag in the middle. Once the ribs and rear spar are clecoed in place, it will need some support in the middle to remove the sag.
At that point, it will be possible to get it completely level along the complete length.
Put some masking tape on the aluminum angles to protect the spar when clamping it.