In the 454's early days GM had an inherent issue with valve train noise. My brother bought a brand new 1974 454 Suburban with the same problem from day one, the dealership never did figure it out. Fortunately for him he was half deaf from a Vietnam GSW, he was good with it.
I have a tick in my BBC T-Bucket, currently changing over to a roller setup, curious to see if it goes away. I originally thought it was a roller rocker hitting the VC on the top side, but not so sure after grinding additional clearances and not seeing any new witness marks. I'll find out if it's an oiling issue when I fire it up.