The Ross Performance Parts Nissan RB Twin Cam Head Drain Adaptor is designed to help prevent potentially dangerous amounts of oil from pooling in the back of the head.

Excessive top end oiling is an inherent design problem with the RB platform when the factory oil pump is upgraded or on engines that see sustained high RPM use. The oil drain holes in the head are too small to displace the increased amount of oil being delivered to the head.
This can at best lead to oil being lost through the cam cover vents and PCV system, through to a destroyed engine from oil starvation when all of the oil is stored in the cam covers instead of the sump!

It’s recommended that engine builders install a correctly sized oil restrictor in the head when upgrading the oil pump which will further help reduce the risk of excessive top end oiling.