tomc9770,

You haven't told us if these are hydraulic lifters or solid lifters. It would be more common for them to be solid. Solid lifters that are set loose will clatter until the engine warms up and the clearances diminsh which will quiet the clicking. What does the machine shop say?

My WAG is they are solids that were set when the engine was on the stand and they need to be adjusted now that everything has run awhile and seated.

Stuart