The age old coil mounting and spacing method that has been discussed on here from the beginning and RCOnline before that is to get the magnet of the flywheel in the position of the coil mount.

Place a business card over the magnet and the coil on top of the business card. The coil will be held in place by the magnet.

Then attached and tighten the coil.

Remove the business card.

I have done them this way on magneto ignition engines for many years and never any trouble yet.

Business cards are generally in the .010" - .012" range

The standard dimension for weed whackers and chainsaws is .3mm or .012" in the service manuals