Under which act we can perform court marriage if either partner does not have proof of religion?

I am an Indian girl planning to marry a German boy whose father is German and mother is Thai. He has stayed in India for about two months in total over multiple visits in the past year. We are having a traditional Hindu marriage in a few months. I would like to know which marriage act will apply to us, considering I am Hindu and he lacks proof of being either Buddhist or Christian. Do his multiple stays qualify him for the 30-day mandatory stay before registration under the Special Marriage Act? If we can somehow prove that he is a Buddhist, can we obtain a marriage certificate based on our wedding invitation card within a few hours of registration? What would be the best scenario for us to marry legally as soon as possible?