For me HSC was harder to get a grasp on because there was more stuff to know. Other than that you should be fine and start with a clean slate in year 12.
There is only bits and pieces of prelim that you will need to know.
You will need to know all the Moving About stuff regarding equations of motion and a little bit regarding momentum. A few things in Cosmic Engine will be required (such as Kepler's Law of Periods, etc). Quite a bit of the electricity and magnetism and induction stuff in Electricity in the home will be needed. You'll need to know EMR in depth so you can understand a few other things in HSC.
There's probably a few more major things from prelim that you need in HSC, but I can't remember all of them at the moment from the top of my head.