engine knock/rattle 360

Hi all

I have an engine knock/rattle hard to explain in my 360 that is there when cold but seem to disappear when engine gets warm.

Engine has only about 50 miles on it, it has

-stock bottom end (new bearing, shot peened rods)
-.040" oversize piston (wasn't blueprinted but briefly remeber seeing KB 10.5-1)
-Mechanical cam
-solid lifters
-Hughs roller rockers

Have had abit of a play around once knock began...Have pulled head off left bank and all seemed fine (pistons, bore, valves, valve springs etc.) re-installed head, double checked valve clearances, no bent push rods, timing is fine. Started it up again to day and sound is still there, pulled ignition plugs one at a time and no change in noise.

Any ideas or suggestion would be great at this point??

Sorry about my dodgy typing!