I wish to relate a recent experience that may help. I have a car from 1963..lets just say its not a MOPAR... that I was convinced had a bad valve. It had a real nice distinct tap on start up. As the car warmed and we were on the road it would soften out. I was all set to get under the engine's skin when I was talking to my uncle (an old hot rodder in his 80s). He went out to the car and placed his hands on the engine. After one or two repositioning of his hands around the valve covers etc. (Yeah it looked like he was healing it) He told me to put my hand on the rear of the exhaust manifold where the mani and pipe join. Sure enough I could feel a hot jet blast on my hand from a small hole in the gasket and it sounded dead to rights like a valve. I put a mirror on it and found it. Should rule it out...could save some trouble.
If possible, run the engine without valve cover and push each of the valve lifters firmly with your thumb, wooden block or equivalent. You should hear a change in the noice or "feel" it when you hit a faulty lifter, spring etc.
When I was in Chrysler tech school long ago, we were taught that lifters are installed offset to the cam lobes, the bottom of the lifter is convex, and the top of the cam lobe is tapered. Those 3 things cause the lifter to spin on the cam lobe. During the 1st few minutes of break-in, each lifter and cam lobe become mated by wear during spinning. If replacing all the lifters, that relationship needs to be reestablished with a new break-in. However, if you've been able to replace all lifters without doing a break-in, and the cam was not damaged, mo-power to you.
I had a 1970 Plymouth Fury with a funny "tick' that seemed to come from the top of the 440 motor. Drove me crazy. I finally found it to be a small exhaust manifold to block gasket leak. Sounds nuts but happened to me. Maybe?