Anyone ever done this and what were your results? I know there would be a loss of combustion efficiency but that doesn't always result in power loss.

This is more theoretical thinking out loud but here is the reason I ask. If you were to revise the left or right spark tube to instead exit the cylinder head at what would be the center of the spark plug tubes at the top of the cylinder head, you be much more free to get the valvetrain geometry more correct. Given there is already some misalignment in the z axis that can only be modified with offset lifters or adjusting the lifter bore spacing, you could at least get both pushrods in line with the lifter bore angles in the x-y plane. Also, it definitely seems like Steel rockers give you best chance to get the most clearance as well since you don't have to use as much material to make them work well.