Thanks everyone, I decided to sit out the 600k and might do a shorter Brevet closer to home. I have not done a long ride in 2 weeks and have been nursing this thing for 9 days, so, the loss of fitness and lack of riding is getting frustrating.
The afflicted skin surface is good and the deeper infection seems almost gone but still a bump and a little tender. Fearful of erupting the volcano on a really long ride, I think a 300k might make more sense overall.
I am going to use chamois cream (laniseptic or utterly ridiculous cream) on all rides now as I do think dryness and cracked skin might have allowed Staph or whatever bug in causing the infection.
I do think there is something about the saddle angle to look into.....after a visit to my Chiro....I had a spine injury years ago from cycling and this sounds the cause as I have had ongoing issues over the years. One of my earlier posts might not have been clear. With a "properly" centered saddle, my left cheek is deeper into the saddle than the right cheek (right ischial tuberosity), which just hits the right, rear rivet on my B17 Champion series. Rotating the seatpost a few degrees CW (right) better centers both my cheeks into the pocket of the saddle. Weird. Anyways, I would not have thought of this w/o unterhausen and Machka's input. I know the distance from pedal axle to sit bone placement on the saddle and distance behind cranks by heart..saddle always centered.....B17 slightly up....Berthoud level...one thing I never really gave much thought to is our bodies can change. The other possiblity is that I started riding my racing bike a little bit and man, those 23mm tires at 110psi do beat you up but I don't ride that thing very far....maybe 40 miles max. I still prefer the cushy ride of my rando rig even if it is slower.
Thanks to all for the words of encouragement and suggestions.