These are too small to bother with porting, or billet wheels, or really anything. You aren't going to get anything worthwhile out of upgrading a K04. The K04 on our T5's is considered best version of them all, and way pretty much the last K04 for production cars. Even VW has moved on past these now for new cars.
Just a rebuild to refresh an old turbo. No idea on the specs of the coating except 2000*F + rated. Was $100 for the manifold in and out and $100 for the downpipe outside only.