hard or soft copper line for a valley oil gallery bypass line?

I agree with your last statement. It is beyond you. Deniers do not want to admit that it works so there's no sense in even trying to convince you otherwise. Just do the modifications and see what happens.

Jad, exactly what end user proof do you have that the crossover does anything? Your own personal experience please with some kind of industry (say SAE or similar technical paper) that shows the crossover slows down the oil to save the bearings.