There is a massive amount of wear inside that unloading auger. I'm going to guess that if bolts could hold up, the kit would be to bolt it on. It is a pain to weld on the end of the auger since there is usually nothing to stand on easily. If bolts would have been easier, but they want you to weld, it, I'd weld it. Don't re-invent the wheel.
That pin that goes to the right angle gearbox up in the diver's helmit - those pins have to be stainless or they won't last. So, maybe if you used some stainless bolts it might work for you.
So hypothetically, lets say you do bolt it on. A couple bolts come out and the flighting is no longer connected. What happens next?