I can't say much from having any experience with the x50 Seibon Hoods, but I remember some friends having Seibon hoods for their IS300 that didn't have the windshield washer holes. While one of friends had to file the holes a bit bigger to fit them in there. Assuming there should be holes, it should be an easy install. The washer squirters should snap right in, then reattach the hoses.
Also, it's a peace of mind to have hood pins as an extra safety measure. Generally, it's not 100% safe to trust the hood latch of any aftermarket CF hood or fiberglass hood for that matter.
You can purchase Aerocatch hood locks which look the cleanest in my opinion.
2002 Graphite Grey Pearl Under Contruction Since 2006 LOL