The groove in the center camshaft journal is machined deeper to help compensate for any potential wear that occurs in the cam bearing that can potentially close up the stock depth groove which will subsequently shut off the oil supply to the topend. On my end, it’s easier to simply add a groove to the center cam hole in the block and circumvent completely having to route the oil to the cam journal and then back to the block again. By design, the factory topend oiling system has a built in oil restriction at the cam journal whether it's by way of a crossdrilled camshaft or a grooved camshaft. Any cam bearing wear with the newer bearings restricts this oil flow even further; hence, the different methods in which to get around this wear issue.
Regarding adding restrictors at the rockers due to modifying the oiling system for an increased oil flow to the topend, it’s much easier to restrict for an excess of oil than have to deal with the lack of it. If the rockers are pressurized rather than allowing the overflow tubes stay in place, then the restrictors may not be needed. I still run overflow tubes on some Y builds so the restrictors need to be in place in those cases.
The 471 heads were the only heads for the Y that came from the factory with hardened exhaust seats. The 113 heads need hardened exhaust seats added for long term use of unleaded fuels.