Popping sound from valvetrain

[Tahoe540]

I had a cracked Bowtie BBC block so I bought a new Dart block. Used all of my old parts except for new rings. I had no issues with valve train when I dissembled the motor. I heard the pop when I was adjusting the valves. I am turning it over by hand as it is on a stand. I have moved the lifter of a popping number 3 cylinder to number 1. Noise stayed with the same valve so it is not a lifter. There is no noise when I remove the rocker from the popping valve. I have plenty of retainer to seal clearance. I have taken the spring apart and do not see any issues. The number 3 and number 7 exhaust valves the pushrods is barely touching the head. Good enough to make a scrape mark. The even side has plenty of clearance of every pushrod but I have one popping on the even side
Any ideas of what could cause this or other things to check?

[bobmc]

to clarify, the problem is 1 particular valve-spring-rocker combination makes a noise when cycled? separate issue is pushrod to head clearance on other cylinders? you swapped lifters between the noisy valve and another with no change, so swap the spring, retainer, locks and especially the spring cup or locator

[tenxal]

I would be very suspicious of the valve lock and/or the fit between the lock and retainer. I've seen this a couple of times and it's been the valve locks that were dinged up. Be really careful, here.

[econo racer]

What heads are you running?