If you are tubing or bushing the block then you can block the line at any one of 2 locations. Just as long as you cut the flow to the drivers side. Again this cuts the velocity because you cut the leakage. Be careful if blocking the line at the end of the passenger side that you get the pipe plug positioned so the it does not block the feed passage down to #1 main. I usually grind a notch in the pipe plug to allow the oil to still go down to the main, but cap the line and still fit under the cam thrust plate.