DWG 11 clearly shows that the lower bolts have washers under the aft heads, and upper bolts get a washer under the nut on the forward side. But - the lower bolts have a gusset under the nuts. Thickness of the washer and nut it is 1/8". Since the all bolts are the same length, an additional washer will be needed or the nut will bottom out on the bolt shoulder before clamping on the upper bolts.
"Proof" This picture clearly shows an exposed bolt and a tight bolt with nut and two standard washers. I will reconfigure with one washer on each end.
Get some extra washers, and make a note on your drawing to put washers under the heads of all the main spar bolts. You will
need them. (edit)
BTW - I machined two progressive sizes of burnish pins to burnish/align the thinner webs. There were lubed and driven all holes and resulted in removable bolts that were assembled with no chilling.