My ticky-tock-tock

[Ou812]

Try a little soapy water out of a spray bottle around the exhaust manifold. If she is pushing any pressure it will rear it's ugly head

 

[iamdub]

... the tapping often begins a few seconds AFTER the engine starts, then it lasts until the engine gets to about 70°F.

Yeah, that pretty much rules out a drained lifter. But, this is good news since the other likely causes are normal and harmless (piston slap) or essentially harmless and easily fixed (exhaust leak).

When checking the manifold bolts, don't forget about those on the Y-pipe flange.