I loosen the locking nut and turn the screw alittle on the rocker arm.
Originally Posted by Pre '68 Dave
Originally Posted by alltruck72
(tightening a few turns then lock them down)

What do you mean by this statement? If someone has put hydraulic lifters in your 261 then you could tighten a few turns (although 1 1/2 turns is recommended) after the push rod slack is removed.
With solids you would use a feeler gauge.
With solids if still noisy after adjustment you may need to reface the valve end of the rocker. They wear where they contact the valve. If worn a feeler gauge bridges this wear while adjusting and will give you a false reading.