The actual spec is .2mm btdc, points gap .35 - .4mm, plug gap .4 mm.
If you take an old spark plug with the same thread as yours (any number will do but long reach is better. I think a lomg reach plig will screw in far enough to toch the piston top. If not, try bending the side electrode out.
It is important that you clean the threads enough to turn the spark plug in by hand. Screw in the plug until the piston touches it as you approach tdc. Be gentle! Back off the spark plug until the piston will just roll over tdc with a slight wiggle of the spark plug. Now turn the magneto counter clockwise 1/2 turn, screw in the plug 2 complete turns, then continue turning ccw until the piston touches the plug. This is where the points should open. You can make a mark on the flywheel and crankcase if you wish.
If you need to work on the points, the magneto comes off if you remove the center bolt using a 3/8 impact. This is a LEFT HAND thread so be aware.