Indian OCI Hindu by religion need guidance to get married to Morccan Girl who is Muslim by religion

Since you are an Australian provisions of Indian (Hindu / Muslim or any other) Marriage Act(s) do not apply.

However, how does the Moroccan Muslim girl stated to be Indian  ???

It is better to consult a local prudent lawyer for proper advise.

You can follow the as per the procedure of The Special Marriage Act of 1954 is an act of the Parliament of India. The Act was enacted to facilitate the civil marriage of inter-faith couples. It provides the people of India and Indian nationals in foreign countries a special form of marriage, irrespective of the religion followed by either party.

Every marriage has two different aspects First and prime is the performance of the marriage ceremony and other is its legal enforceability.

As far the Performance is concerned you can get perform your marriage ceremonies in India or any where else under local Marriage lows. As in India Under Special marriage Act 1954. By that you both do not have to change your respective religious faith. 

However, about the enforceability of it in a legal term, is by its registration with the Registrar of Marriage and then after getting a Marriage Registration Certificate as a proof of marriage. However, there are more other things like Photographs and other people invitees attending the marriage ceremony are the secondary evidences to a marriage but the Certificate of Marriage has the direct effect to prove a valid marriage between the two parties as a prime evidence. 

Admittedly, both of you are not Indian citizens. Then why marriage in India?