That's good news about the strut doublers. You can just slide the ribs over the rear spar from the tip, starting with rib #3. Cutting the bevel with your table saw should be very easy, and no cause for concern. Just set the blade at 10° or whatever angle you decide on, set your fence so pushing the spar through will just skim off the tiny edge of the ply web & remove mostly the sliver of spruce off the spar cap. The thing that helped me was setting up supports at both ends of the spar, so I did not need another person helping.