Injen and AEM also make Cold air intakes. You won't see any gains in HP with a short ram.Especially not one worth the $$ for them.
Any intake you purchase will come with instructions for installation. Plus you have the forum if you have any questions about the install. After all, it is only an intake.
This will give you more in depth instructions for the Stillen install.
http://www.the370z.com/intake-exhaus...de-ak370z.html
Good luck with your decision