After some back-and-forth with friends on other forums, I morphed the design into simply installing the bronze bushings in the swingarm, welding a plate to one end of a piece of 3/4" hardened bar stock, threading the other end of the bar, and fabricated a companion capture plate for the opposite end of the shaft with a Nyloc nut to retain it.
Thanx to my custom knifemaker friend, Enrique (who did the MIG welding and showed me how to use his lathe) here are the results- (Note the lubrication port (1/4" bolt at top) for 140W bearing lube)-
The assembly takes two bronze thrust bearings (with captive o-rings to keep the lube in check) between the swingarm face and the frame plates.
So, with my retrofit kit, (I've got 6 of them set aside now), the swingarm forces are transmitted through a lubricated, precision fit between the 3/4" bar stock and two 1-1/2" long sintered bronze bushings, to a 4-bolt security fit to the frame webs AND the 3/4" diameter precision fit between the spindle and frame plates, all held in tolerance with a 3/4" hardened Nyloc nut that can be precisely shimmed and checked at the thrust washer interface. "A bit" of an improvement...
Note to any featherbed purists on board: If you believe I've destroyed the legendary handling of the frame with this modification, I'll only agree to disagree, agreeably. I don't believe that adding rigidity and precision to the swingarm's connection to the frame distracts from any aspect of structural performance of the assembly. If you believe the inherent flexibility in the original design somehow acted on the original assembly to moderate excessive forces imposed on the relatively mild tubing materials and small diameter interface hardware, to produce the legendary ride, you don't have science to back you up.