What's this for and where's it go-to. The big black part.

Thats the crank case breather. The pipe vents to the inlet manifold IIRC

That's right it goes the the inlet on the efi setup , but I'm using carbs , so just put a small filter on it?

Make sure whatever exhaust manifold / front pipe you are going to fit clears it first before you decide to keep it, there are other ways to set up the breather that take up less space if needed.

Yes mate, You could link the rocker breather and bottom breather into a catch tank with a filter on it as well

Ok thanks , I'm just using the one that came with engine to get me moving , cheers guys.