There are as many opinions as there are Skylines There is a HUGE discussion on the Australian Skyline forum that goes into painful depth, but fails to reach a universally agreed conclusion. A search here will give a lot of opinion, too. Personally I think a return to the sump UNDER the oil level is totally wrong, I have done it quite differently. IMO half the problem is tired engines that produce a lot of piston blow by. I would use a head feed oil restrictor, for sure.
Drill out the oil return galleries in the head and block is pretty much self explanatory. As is machining (die grinder) around the oil return galleries to facilitate access for the oil to the return bgalleries.