Any question answered...

With a steel fork and a 27 mm bolt you might even have to cut down the nut, or use a shorter one. They were introduced to deal with the really deep carbon forks, I am sure your steel fork won't be that deep.

I was thinking of the length of the brakes bolt rather than the nut . I.E. Whether it'd be long enough to clear the front of the Crown with 6 whole turns.

This is to your advantage, as the crown is likely to have loads of space for the nut. If you're to avoid changing the centre bolt, the front of the nut is going to have to get within about 6mm of the front of the fork crown.

Perhaps I can borrow someone else's sram brake and see how well it'll fit