Vallalar secret alchemy is very similar to what is experienced in the practices of Tummo and Tsa Lung Thigle.
The way to experience what he describe is different and does not requires physical Inner Yoga skills. In the teachings of Clear Light Tantra Dhaya Dorje brings forward knowledge of Vallalar king of the Siddhas form South India and the Maha Siddhas Yogi/ Yoginis of the Northern countries of the Himalayas.
Vallalar king of the Siddhas says :
The true occupation is to cause everything to self-create by one wish and will.
This, by the discovery of one realization of non-consuming air;
the ambrosial air circulating inside Sushumna (central channel) and the eyebrow center;
the deathless ether which is causal fire near the heart center ;
the non-flowing fluid which is the causal ambrosia ( the drops) transforming the blood to coagulate, and the semen concentrated in the medulla oblongata, connected to the pituitary gland.
One day the whole world will realize these four secrets coming from the siddhas tradition, leading to perfect bliss and supra-active alchemical powers.
Page 114 of my book Grace Light Yoga in 5 steps by Dhaya Dorje available on my web site or www. lulu.com