MY99 impreza gt turbo
Complete scooby exhaust system and Open dumpvalve.

I am planning to fit a Gruppe S manifold or Gt spec manifold, wich one should i choose?
I also want to up my boost to about 1.2 bar with a manual boost controller.
Are there things i need to think about, to be extra carefull with?
Do i need to remap the ecu? (Hope not)
I have read some things about the knock link, that it stops working after fitting another manifold?

Any advice would be welcome.

Thxs in advance.
alex