It's the genuine Nissan water pump, that was put in N spec models. From what I can see it was made for R34 Nur models however it is compatible with R33 GTR's as well.
Stolen from wiki
"RB26DETT N1 is an upgraded version of the standard RB26DETT engine. It was developed by Nissan Kohki's REINIK division for NISMO and N1 race cars. The standard RB26DETT, although known for its durability, proved to require too much maintenance for Group N (N1 class) racing conditions. REINIK started with strengthened RB26DETT block. N1 block is identified by its 24U number stamped on the block (05U standard blocks). The cylinder walls are thicker and water cooling channels are enhanced to increase flow. It also received an upgraded oil pump and water pump, to improve the cooling and lubrication for race conditions."