I also will reserve judgement until I can see the pictures, but I suspect that the plugs are normal from the description.
The technique of reading plugs as you have described is also called "cut clean". It was beneficial in days long past, but isn't near as helpful as other tools today in determining air/fuel mixture. You can get a much more accurate picture with a scan tool while driving.
To properly do a "cut clean" required room on a race track to run at heavy throttle for a while before hitting wide open throttle, holding wide open throttle for as long as safe, and then shutting off as you have described. The idea to have no other factors involved to dirty the plugs.
I only did the "cut clean" technique a few times. I soon found other ways to give me the information I needed, at least close enough, to make my evaluations with that I felt were safer for a street rodder. When I could, I used an exhaust gas analizer. When not available, I would use atrificial enrichment (feeding metered propane). If you felt a boost in power by adding propane you were too lean. If you didn't feel a boost, you may be OK or could be too rich. I would richen up the jets (or other measures) until I was barely able to feel the increase. Anyway, as primitive as is was, it worked for me. I would have loved to been able to read a scanner instead.
