small block cam issues...rattley new engine!

I too agree.... if different lifters have been tried, then the pushrods are next. How could the rocker manufacturer rule out them being a bit too short without actually measuring the lifter preload in the engine?

What weights of oil are being used? Light oils tend to leak out of the lifters more easily when setting for a while. Synthetics also are more prone to make this happen; they are a lot thinner at typical cold start temps.