Ideas on what's causing my click/tick/rattle noise?

Lots of good ideas offered by lots of other guys.
I just want to add that, to a trained ear;
>noises inside the oilpan usually have a bass tone to them, more of a hollow knocking
> noises in the valve cover usually are more of a metallic clacking, unless something is hitting the cover, but you can feel that under your hand.
> the crank should have less than .010 endplay. If it gets too much bigger it will develop a random tapping as it bounces back and forth. You can measure this at the balancer.
> wrist-pin noises are rare, but are a double tap caused by the thrust reversal at the top and bottom of the stroke; it is a very distinctive noise.
> Valve-lash you are familiar with. But slantys are a unique case. The rocker-arms are fairly soft, and the valve stems are very hard. So slanty arms eventually develop narrow grooves in them from the stems sliding back and forth. When this happens, you cannot use a regular feeler any more, because it will span the groove, and the groove depth under it, will be added to the lash. Therefore you need a narrow feeler to lay in the bottom of the groove.
Your builder should know this and should have re-ground your arms. But ................ you never know.
> the fuel pump noise, if any, is easy to mistake for other noise, but easy to prove.
> as for the cam walking back and forth, I don't know what that might sound like nor if it is even possible to develop that much play.
> another thing I don't know: if you install solid lifters in a hydro engine, is it possible for the solids to leak oil when they rise up with the cam-lobe? IDK.
> the factory engine had the intake-manifold bolted to the head together with the exhaust, using special conical washers that were designed to maintain their tension as the parts, all three, have varying rates and amounts of expansion; So those washers will act as springs. If you have not reused those washers; I can only guess what will happen.
> if you have forged pistons, I suppose piston-slap could be an issue, if your engine never warms up, or the skirt clearance is too great. This noise usually goes away as the engine comes up to temp; actually, as the pistons swell up. You can check this by, for testing purposes, by blocking off airflow to the rad, until the engine temp comes up to about 200/210. The noise should get quieter then disappear, as the temp goes up.
But this noise comes in multiples of three per revolution, lol, so has a distinctive tempo, as compared to most other noises.
> exhaust ticking is the most common. It follows rpm but often disappears on engine deceleration with closed throttle. And it gets louder as the engine is asked to work, with increased throttle. If your ignition timing is late, the mixture, may not finish burning inside the combustion chamber. If it is still burning and expanding in the header, it is gonna try to get out anywhere it can. You can often find the place(s) by the tell-tale soot marks.
> and finally, a wildcard; ignition snapping noises. Could be a wire not fully seated. Could be leakage, but then you would also have rough-running, especially on a 6-cylinder that only fires three cylinders per revolution; to lose one is a very big deal.

That's all I got, hope it helps.