If you only anticipate doing this job infrequently and don’t want to invest in the ring tool there is another way. Just move the armature heals out flush with the machined surfaces on the mag plate, all done! Now if you care to check the set-up or perhaps want to get closer , apply a layer of paper masking tape to the heals , install the flywheel and rotate, move the heals out until you just see a scuff mark on the tape.
Just use your fingernail !! Run it up and down the face of the coils and if you feel it snagging even just a bit going up or down…. realign the coil for a smooth travel of your fingernail up and down the face of it !! Cost $0