FWIW, I don't think I've seen a non cam'ed L36 pass the 200 whp mark.
As far as the valvetrain goes, ZZP ER rockers are the best ratio you can go with. 1.9'* are too high a ratio and you end up with a more peaky powerband.
Check out Easy Performance'*
tech info article on the ER ratio.
I saw a hv3 mentioned and that mod would compliment rockers and exhaust work nicely. Without valvetrain work though, it isn't recommended.
What are you looking to spend and how far are you looking to go as far as DIY stuff goes?
There are various threads on how to make your lower intake manifold more efficient.