Thanks, gents.
Daniel, I have no idea what these brushes will fit. I was shown the drawer that housed them all and I simply chose the two smallest sizes they had, both of which had the same spring.
It does jump around a lot less.
There are long threaded 1/4-32 spark plugs available that will solve most of what you are looking for re putting the plug more into the line of fire (fuel/air). I can't help but wonder if having the plug tucked up in there so far is helping, hurting or not mattering regarding fowling?
Power isn't an issue as this is no racing hemi!