There is some confusion in these last 2-3 posts about Sanborns mods. If you can, go over to Mopar chat and read his complete mods. On my engine, the line going to the front oil boss is 8an which is 1/2 inch.
The pictures shown are how to front oil a stock block. Sanborn rarely used stock blocks and when he front oiled a race block like an X block or a r block, the feed lines were external directly from the oil filter supply. He shows how he threads the passages that enter and leave the oil filter area.
Second the front oiling is not to oil number one main only.
Sanborn does block the feed passage from number one over to the drivers side galley as he claimed repeated failure of the front rods if you don't.
But the front oiling according to Sanborn was to stop what he called turbulence in the galley. He used that word. So even his theory was that there is distribution issues in the galley. The second oil feed to the front was to send a second supply of oil to disrupt that turbulence and even out the supply to the main bearings.
The pictures shown, show that Sanborn used a bulkhead fitting to bring the supply to the front of a stock block. On a race block, his front feeds were 8an and done externally to the front feed boss that those blocks have cast in.
His supply lines came directly from the oil filter area and those lines go to an external large oil filter using 12an hose. This is how I have done my engine using a nascar race filter with 12an lines and an accumulator. On an X block it is difficult to use a hose larger than 8 an because you have to make hard turn in the fuel pump area to connect to the galley. If you use a motor plate it is even more difficult. I believe that's why that boss was moved to the china wall on the r blocks, easier access.
The crossover line to the drivers side galley was optional as Sanborns racing class required wet lifters, so in this case the crossover was only meant to get some oil over there. Not to help the bottom end oiling like the Atherton crossover.