I have a Greddy header and the installation was pretty straightforward. Remove the o2 sensor first, mine was a pain in the ass to remove. It would be good if you have the sensor socket but an open wrench should do it. You might need to drain the coolant so you can disconnect the water pipe, depends on your car.

Removing the stock parts takes most of the time, after that, it's a piece of cake.

Will
99 Black GS