There are many ways to make the plate fit properly. I chose feeler gauges because they were already at hand. And the shim is only needed during the setting process, as are the feeler gauges.
You could also peen the plate (mashing it thinner to grow in radial direction)...
Just trying to learn but I don't understand. How do you determine where to put the shim and I thought you would need to leave it in ?
You need to leave the shim in during the gap adjustment and the 1:4 timing procedure. Once the main plate is tightened down, you don't need it again until the main plate is once again loosened.
The main points plate fits within the engine case bosses and the engine case also registers the point cam position. These are solid reference points.
The points rubbing block registers to the main point plate. And each point set has a spring putting force between the rubbing block and the points plate. If you move the main plate laterally by spring action(don't confuse this movement with rotational positioning), it changes the point gap while the rubbing block rests on the point cam. The point cam alternates this spring action as the crankshaft turns.
By confining the main points plate, to register accurately with the engine mount bosses, the gap setting remains unchanged as the point cam rotates and the point spring action changes dominance from side to side. The registration must then be held constant, while the plate is rotated to achieve proper point open timing.
I believe I usually put the shim at the bottom right engine mount boss. However, the geometry may demand placement at the lower left, if the timing slots of either point set prevent hit their bounds before the proper timing adjustment. can be achieved. Unfortunately, if you find out that the 2:3 set can't be adjusted, you must move the shim, and then start again from the beginning, adjusting gap of both, do 1:4 timing again, and then 2:3 timing.
If you happen to have a loose plate, you can sometimes see the whole plate move side to side while the engine runs at low speed.
Further, for ever thousandth that the plate is made undersize w.r.t. the engine bosses, that is the amount of variance that will be applied to each point gap as the points cam rotates 180 degree. If the gap changes, the point opening timing changes as well. I forget the timing degree difference each thousandth of gap setting change creates. There would also be a cam profile relationship as well. But, an understanding of this detail isn't needed to solve the gap and timing set issues.
This is so easy to show with an example machine in person. Textual concepts don't always translate well, though. Perhaps I should work up some pictures and drawings. ...in my spare time.
