OK,after consulting with my Engineer friend and he running some numbers,had the following suggestions, to be tried incrementally.
The swing arm bushings are adequate, but pivot bolt/spacer need lubrication. No da Right?
Gusseting of swing arm, in area of the intersection of pivot tube and side tubes, in an arch shape with 10 gauge steel, increasing swing arm rigidity by a factor of 2.This may make the swing are too stiff, and eliminates almost all of the flex. Also more labor for me.
Option two is to cross brace swing arm, about 2 1/4" down from pivot tube, between side tubes with equal or greater size pipe.(1" Black Pipe).This works out to be about a 30% reduction in rigidity from above, which may be enough. Less work for me.
He also had an interesting thought about the front wheel. Leave the stock 18" rim and low profile tire, but add 4 crimp on spoke weights, directly across from each other, spaced evenly around rim.Weights of maybe 3/4 oz or 1 oz. Then balance wheel with a 5th,of what ever size needed. This will give the front wheel more mass, and more difficult to upset at higher speeds,but retaining most of the maneuverability of the smaller wheel. Pretty cool thought Huh? Cheaper than a new tire/ rim.
Sparks will be flying in the Garage tomorrow Boys, I'll let you know. Dan