Disk brake conversion, ball joint hitting lca

Yup, that is in fact the the steering stop on the lower ball joint, and it is supposed to be there.

I actually had the opposite problem, with the wheels being able to turn so far that they were contacting the frame while I was running a wheel combo others had without that issue. I measured a half a dozen different lower ball joints, and found that the height of that steering stop varied greatly depending on the manufacturer of the lower ball joint. Some barely had a nub at all, others had fairly tall ones like the one you picture.

So, given that the steering stop height is so variable by the manufacturer of the lower ball joint, I would just trim it down if it’s getting in the way too soon.