If I remember correctly, the ribs and front spar are riveted to the skin first without the rear spar in place, so that you can buck the skin to rib rivets. Then the rear spar is put in place and at this point there would be no access to the back of those spar to rib rivets. It may be possible to change the assembly order slightly to avoid this, but I would just go with the plans and keep it simple.
Chris