Everything BCRider said.

And with regards to welding a disc caliper mount onto that (I'm thinking) aluminum fork it seems like a great way to anneal the alloy in the zone (which would then see significant braking forces, adding insult to injury) and probably dis-align the fork in the process. A pretty bad idea, that one. -- edit: if we are in fact talking about brazing a new mount on, that would make more sense, but still nowhere as much sense as better calipers.