I currently have a student doing exactly what you want. He has an Australian PPL and an FAA certificate based on that license but wants a stand alone FAA certificate. He has an FAA medical and will take the written test shortly. The ground reference maneuvers are straightforward enough but you will need to practice the specifics as described in the FAA's Airman Certification Standards. I'm an Australian flight instructor and LAME who moved to the USA a few years ago and now have a flight school and maintenance business near Sacramento. PM me if there's anything I can help you with. Depending on your situation, you may need TSA approval to undertake flight training here. The process is very straightforward.