Eh...actually we think they will probably end up fitting. We just haven't test fit them on a GT500 yet. We are getting one here soon to test them, but until we actually test fit them it is better to play it on the safe side, hence the note.
If you have a big brake kit we always recommend buying 1 wheel without the tire mounted and test fitting before buying the rest of your wheels. That way if it doesn't fit you can return it no problems.