Assembled the front and rear halves of the center spar and test fitted it to the wings.
Returned the center spar to the bench and backdrilled the top rear rivet line that joins the front and rear halves in front of the seat pan rivet holes. added the extra rivets between them to give the prescribed 20mm pitch.
Parted the halves and set the A5 rivets in the rivet line at the front of the top doubler that holdes the front web to the doubler.
Set some of the solid rivets through the front spar caps.
Temporarilly assembled for trial fit to wing spars
Only set some solid rivets ready for another trial fit to the wings