Years ago I had an AMC Hornet with the same engine - 258 ci - 4 liter
It started having that same noise. I tried replacing the lifters, no help.
The noise drove me crazy, I spent all that money, having the shop replace the lifters & push rods, and turned out not being the problem
It turned out to be one of the rocker arms, where the pivot & arm met, one was scored, making a tapping noise.
I could have saved hundreds of dollars & bought one 8 dollar rocker & pivot .
Hope this might help. Good luck.