Got a longeron yoke in from Brown tool. Used it to squeeze the #1 ribs to rear spar (AD-4-6 rivets, 6 plcs). Tried an AD-4-7 rivet in one of the 6 places...it formed an OK head, but would be prone to clench. The AD-4-6 heads are just a little bit less than 1.5D by the time the squeeze has created a 0.5D thick head. Decided that the AD-4-6 heads are OK...it's what the plans call out!