I don't think this is possible for a multitude of reasons, one being how large size comes about. Animals become very large when there is not much effort involved in getting their food. Look at all the largest animals to exist, even in recent evolutionary history: whales, elephants, mega sloths, whale sharks, etc. All of these animals put very little energy into living unless necessary.
Out of all things an animal can do, other than fighting, climbing takes up some of the most energy. As a result, animals that climb don't evolve to be big. Another detail to keep in mind is that it is vastly easier to climb the less you weigh; so of two climbing animals of equal size and build but different weight, evolution will favor the lighter one.
But this is speculative biology and we can get crazy. Let's suppose that its limbs are simply half, half. 2 pairs are used for supporting the weight while on the ground. Only 2 pairs are needed to support its weight on the ground as at its largest, it only weighs 1/15 of an elephant. Spread hoof feet, a la elephant, will work best here.
The other 4 pairs will be... weird. For one, the animals climbing limbs will need to evolve from a hoof as did the elephant foot. For two, natural climbing limbs we see on earth will not cut it here as the animal weighs more. I imagine a singular hoof that perhaps evolved a shape similar to a climbing axe.
These limbs will be very powerful, perhaps even twice as much as the legs. The shape of this hoof will also allow for a good defensive tools as well as grabbing high up food or escaping prey (depending on whether it is herbivore or carnivore or both).