I have been making some (slow) progress on my Sig Somethin Extra build. So far, I have the left wing ribs, spars, and shear webs glued. Need to add the LE and TE sheeting before unpinning it from the board.
To keep the ribs square during assembly, I have been making use of 1-2-3 blocks. Normally used by machinists, they are square and flat and heavy enough (relative to the light balsa and ply parts) to stay where you put them. At $17 a pair, they are quite affordable and have a multitude of uses for fixturing during assembly.