Solving "impossible rivet" in arch outer skin

If the inner arch skin is installed first, and the outer skin installed later, the bottom two front rivets of the outer skin become impossible to reach if the top rail is installed in the meantime. To avoid this, I have installed the arch outer skin first. This is fully rivetted into place, with the bottom two rivets on each side, front and back countersunk. The skins and arch rib flanges were dimpled. Just before the top-rails are installed, I can install the countersink rivets. Only the front rivets are installed, the rear holes needed to be left unriveted. This is to enable the skins to be flexed in this are so that the top aft rivet of the top rail can be installed.