Re: blueprinting not hotrodding
if it was a spare, they'd come from the factory sealed in a bag, not attached to the engine..
as far as slant head orientation, it really doesn't matter. technically, it should be so the plug is pointing towards the intake port, so it fires quicker.
i think a lot of people use them because of clearance issues, so they can rotate it whichever way so the plug fits into the frame.