408 oiling advice

I am a firm believer in the A&W crossover tube modification. As for the passage from the mains up to the main oil galley you need to see what it already is. I've had them that were restricted and I had them that were already 5/16. You got to watch for that step in the passage on the earlier blocks. I don't believe the Magnums have the step. But if it does drill it out.
You are plugging the right side (passenger side) passage in the front. The easiest way is to set a freeze plug in the oil galley to block the front passage.
Read the last 10 pages.