Thanks to all who contributed to a spirited discussion. My plan of action is to switch the left hand side to 7/16 R/H threads so I can use the adapter manufacturers larger conical seat nuts to hold spacers to drum and rear axle. Will also use locktite on those larger conical seat nuts, properly torqued, per adapter makers instructions. I'll consider my repair tempoary until I decide whether or not to upgrade to BBP disk brakes.