Re: #1 Plug is Fouling.
Glad to see the running valve lash set. If anything, as you do it, it's right and you can tell if you have valve train problems.
Sounds like you have it under controlled.
Either you have lack of spark problem, or lack of compression, and of course plug fowling by contamination. One cylinder, tends to rule out fuel delivery, unless you have other rich cylinders. What do the other plugs look like? how do you drive the car. You could be running rich and #1 is affected more than the others. After all you do have leaner and richer cylinders.
Heat range may help, what heads do you have, but why only one cylinder affected? How old are the plugs? Install new plugs, take the car out and run it, try to find a place where when you do it, you can shut it down without stopping or idling the least amount. Remove the plugs and read them.
Check your pcv hose, if your getting excessive oil in it, you may be drafting oil to this cylinder more than others, depending on your intake, and fowling the plug. Move it to the rear or manifold vacuum tee or plug it to test. You can clean or replace it, make sure it is the correct one for your manifold vacuum.
Also cleaning plugs with a steel brush, let alone mounted on a bench grinder is not good. Your burnishing the porcelain, which may lead to cracking, but you are impregnating steel in the porcelain causing it to become conductive leading to misfiring. Same reason you do not use steel brushes when welding aluminum, you can see the contamination in the aluminum. If you have to clean plugs, nylon brush and chemical cleaner. If they don't clean easy, buy new plugs. I used to have a 1940 plug sandblaster, don't think that's done anymore.
Be looking forward to your problem being resolved. Good Luck.