You don’t need to time the points to piston movement,since moving the mag plate changes that. If you simply set the points to the proper gap, the magneto timing should be fine.
If you want to optimize performance, time the points so they open exactly 180 degrees apart. That is, adjust one set to the specified gap, then set the flywheel to where that set is just starting to open. Without moving the mag plate, rotate the flywheel 180 degrees and adjust the other set to just start opening.
A simple way to “rotate the flywheel 180 degrees” is to make a mark on the flywheel and line it up with something that doesn’t move, like a cowl mount or a recoil mount. Then use a tape measure and determine the circumference of the flywheel. Measure half of the circumference and make another mark, which should be 180 degrees from the first mark. Line up the second mark with the same thing you originally lined up with the first mark. Now the flywheel is 180 degrees from where you started. Adjust the second set of points.
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