When setting up my 3 gear Summers Bros drive, I took 2 strips of notebook paper, folded them in half and rotated them between the gears and then tightened the idler, removed the paper and the backlash is set, never an issue. This method came direct from one of the top sprint car engine builders of USAC and WOO 410. Gears only see load in 1 direction anyway so it really does not matter as long as there is no binding in the gears