Either get the lady (woud be bride) to adopt Hinduism and marry as per Hindu Marriage Act, 1955 or
Get the marriage performed / registered under the provisions of Special Marriage Act,1954.
It would be better to contact and consult a local prudent lawyer for proper guidance and proceeding.
However, if you are located in Delhi and feel, you may contact me (on appointment) at:
Chamber No 647, Lwayer's Chamber Block, Dwarka Courts Complex, Sector 10, Dwarka, New Delhi Cell # +91 9891152939 email: majjagdish@yahoo.com
The change of religion for Hindu marriage is not good suggestion as that conversion has been held as invalid just for the purpose of marriage by the Supreme Court of India.
I have been looking in to Immigration cases for different countries where the Indian marriage with foreigner or NRIs for the purpose of spouse visa are matter of concern, any wrong step taken under the guidance of fake lawyer will lead you to big trouble so just avoid them.
You can contact me for proper legal consultancy: