Trying to sort out a low rpm only, cold knock on a friend's newly built non-mopar L31 350ci V8. Looking for some opinions...

Symptoms:

Knocking sound occurs on cold start up below 1200 rpm.

Above 1200 rpm noise goes-away all together, even when cold.

When cold the lower the rpm the sound is more noticeable, like 800-1000rpm.

Knocking sound disappears completely when engine reaches 160 degrees.


Additional Info:
KB Hyper 12cc Dished Pistons, 9.7:1 Static Comp.
Hyd. Roller Street cam 224@.050" / .510"
Conventional 10-30 weight oil is being used, has instant oil pressure upon start up.
Factory oil bypass eliminated, running K&N Oil Filter with internal bypass

Engine Starts and Runs great outside of cold knock. Of course it could be piston slap, but it's very noticeable, seems a bit loud too me.

Looking for opinions, suggestions and similar experiences. Thanks!