I want to turbo my L67 engine. So can i just change the intake manifold or do i need to put the ecotec heads too?

You can just change your intake manifold and block off the injector port in the intake manifold or cylinder heads. Please note when doing this that these holes are blocked off properly such that they don't impair air flow. Otherwise, you would have to change over to ecotec cylinder heads, which arguably would be the best approach.