Had a push-rod break in half and a lifter pop out of the hole on my 69 dodge town and country wagon with the 440. Longer anecdote with intermittently rotating rotor, frost plug woes, bent push-rods, and other twists and turns...waiting for the campfire to tell it around.

I had over 200,000 miles on that wagon and, yes, you could hear the valve train for the first 10-12 seconds. On the new dodge hellcats, it takes 3 minutes or so before everything warms enough to reduce the noise to the normal background level. Another good anecdote here with the dealer thinking there was a problem as well, changed a bunch of things including the supercharger, still there.. Turned out to be normal due to the sheer size of the engine parts, operating temperatures, and thermal expansion design requirements. The ex-spouse took the hellcat when she left.