1968 GMC Inline 250 Valve Adjustment

[68gmcdude]

Hi All...
I have a slight clicking/clacking noise so I'm thinking the valves may need adjusted. I found some older posts I've been reading but I saw conflicting information. Some say to tighten the nuts an additional 1/2 half turn after reaching zero lash and some say to tighten 1 full turn. Also, some say to tighten the additional turn with the motor running and some say to tighten after turning to motor off. With that being said, the GM shop manual says to tighten each nut four 1/4 turns, 10 seconds apart (for a total of 1 full turn) while the engine is running. That was back in 1968 so the thinking may have changed. My motor is all original with 55k miles. Looking forward to the advice.