As to the OP’s strange noise....... IMO, it’s related to the cam bearing clearance and or material.

With high spring loads the cam bends slightly, and if the bearing clearance is too tight to allow for this, the cam can start to bind in the bearing bores.
It’s the same situation as when too light/thin of a wrist pin is used and it flexes in the piston pin bores and starts to gall the bores up.
Sometimes you just need more room for things to move around.

This is the test I would do......
Remove the spark plugs so the engine can be turned over manually as easy as possible.
Verify you’re still hearing the noise.
Then remove the distributor and drive gear...... install and run the priming tool, and see if the noise is decreased or eliminated(or if the motor seems to rotate easier) when there is oil pressure at the cam bearings.

I’d be trying to figure out if the noise was related to the cam rotating in the bearings, or the lifters rubbing on the cam.

Another thing that could be done is remove most of the pushrods.
Say, all but one cylinders worth.
This would greatly reduce the friction between the cam and the bearings, but the two remaining lifters would still be rubbing on the cam just as hard.