As I claimed in this post, Spanish Fighting cattle (Lidia) might be one of the most precious breeds for creating a near-aurochs despite its small size and increased aggression/nervousness. But due to the economic irrelevance of aurochs-like features and the continuing crossing-in of derived breeds, many Lidia herds display a number of domestic features such as deviant colour variants and longish, heavy bodies.
Nevertheless, there still seem to be a lot of Lidia bulls that show the valuable features present in that breed, including a very athletic body with a large hump matching the size of that feature in the aurochs (no non-feral cattle have humps as well-pronounced as Lidia), decently inwards-curving horns, a longish or at least not too short skull and a trunk/withers height ratio that isn't bad. Also, although certainly not the most important feature, most Lidia bulls have the curly forelocks described for the aurochs (these are present in a number of other breeds, as well of course).
Remember that those bulls we get to see usually are young bulls not older than 5, so they are more slender than they will be at full age.
Most the totally black bulls have the dominant E^d allele, which is a domestic mutation. The other bulls above are wildtype coloured, although many wild-coloured Lidia bulls differ from the aurochs in having a colour saddle due to lessened sexual dimorphism. Some of the bulls linked above have a correct aurochs colour.
I think Lidia is too precious to vanish without being used in any breeding-back project on a large scale. Surely the biggest problems with that breed is its high potential aggression and nervousness and its small size. But since there are still Lidia bulls and cows that get culled because they don't have the "fighting spirit" necessary for bullfighting there is the chance that one can successfully select for less aggression by choosing the most relaxed Lidia for a breeding-back project. The crossing-in of other breeds, which is also necessary because of phenotypic reasons, will further reduce the level of aggression. For a breeding-back project based on Lidia, only individuals displaying the right colour (no E^d, brindle or other domestic colours), an athletic body with a large hump, good proportions and useful horns should be chosen. Crossing-in of large breeds like Chianina or perhaps the Maltese ox (to avoid recessive colour dilution) and large-horned breeds (I wonder which breed is best - Steppe-type cattle add problematic colour genes, large-horned Heck cattle bring in a domestic body and skull, and Barrosa both). Some generations of selection might lead to a very impressive aurochs effigy that maybe even surpasses other contemporary breeding-back programs because of the high degree of aurochs-likeness that "unimproved" Lidia already have. As you might already know, I would call this improved Lidia lineage and aurochs effigy "Lidia primitiva".