I have done a couple of posts trying to investigate what the Indian aurochs looked like, including illustrations (go here fore the latest). The problem is that it is rather speculative as there is not a single more or less complete postcranial skeleton nor are there any sources concerning its fur colour. However, at least concerning the head we can be sure as there are a couple of complete crania preserved. Using one of the rare photos of a cranium of Bos primigenius namadicusI did a head portrait compared to that of a European aurochs bull based on the Berlin skull.
You can clearly see the cranial differences that are evidenced by the bones. The Indian skull is much more sleek and narrow, while the European one is more massive. The Indian skull has a frontal area that is broader than the distance between the orbitals. The horns are way more longer and more wide-ranging, not necessarily more upright than in the Berlin specimen. These are the hard facts dictated by the bones.
All the other differences between both aurochs on my drawing are inferred from deductive reasoning and comparison with primitive taurine and zebuine cattle. For example, curly forelocks are proven by historic evidence for the European subspecies and most domestic taurine cattle have them, at least the bulls. For the Indian aurochs, there is no evidence on its pelage, but there are not any zebuine cattle on this world that have curly forelocks (at least no purebred ones). In many wild bovids, those living in temperate climate have some kind of ornamenting fur traits such as manes and beards (see bison and many goat and sheep species), while those in tropical climates have short coat and fleshy appendages such as a dewlap instead. This is why my Indian aurochs has no curly forelocks but a slightly larger dewlap than the European one – thermoregulation being another reason to consider a larger dewlap and a bit more wrinkled skin for the Indian subspecies.
Also, I chose to give my Indian aurochs the ear shape of zebu cattle, and used a Watussi individual for reconstructing the face shape, so that the aurochs looks “zebuine” (but not domestic, f.e. I consider the hanging ears of zebu cattle a classic domestic trait).
I think those drawings are plausible reconstructions for subspecies inhabiting tropical and temperate climate, respectively.