the idea is great,but......and it,s a big but for "true" brush alignment the hood will be out of lign.this is because there is a small but appreciateble amount of play between the bush and hood.
to align the brushs correctly you need to do them 1 at a time.the only way to check for correct alignment is then to run the motor up and see where the new brush is marking the com,then move the hood accordingly until the mark is dead center then repeat for the other brush
takes time but it,s the best way

there is a better and fuller explanation on Big Jim,s forum


http://rccars.com/forums/forumdisplay.php?forumid=19ms

also alot of other motor tuning related stuff