Setting Valves on 89 GMC

Give me some tips on setting the valves on 89 GMC 2500 with 5.7 350. I used to set them by loosening off the rocker nut until I heard them "slap" and tightened them back until it quit adding 1 round. Now my hearing has left me and I need another way to set the valves since I can no longer hear like I used to. Also...If you know of a torque spec that will apply to the rocker arm nut let me know.

with the valve closed, turn the pushrod with your fingers as you tighten the rocker arm, when the pushrod stops turning freely by finger, add 1 round.