strange off-idle clattering sound in my 350

[Taibo]

Originally Posted by mattfranklin

Most were about zero lash except for #5, which had one about two turns in. It seems to idle better now, BUT the off-idle noise is still there.

What's left? Rod bearings, fuel pump push rod, exhaust leaks? Motor mounts? Clutch/flywheel innards? Harmonic balancer?

All of the suggestions so far are good, but much less likely than a simple exhaust leak between manifold and cylinder head. Before worring about rod bearings and fuel pump pushrods, check for a leak. You can sometimes find them if there's soot on the manifold but if your engine is covered with crud looking for black soot on black burned oil and grease isn't going to help you.