I know adding spacers is ok (Ford did it as std on the M16 calipers on my car) but how do you seal the plate to the caliper body to prevent leaks?
The one bolt on the flange is a bit of a red herring. The plug with 'O' ring secures the whole thing very well so the bolt is just a 'belt & braces' device. It's very solid.It might be worth adding a support bracket to that, vibration might stress the plate on the head as its only the one bolt.
and once the inlet etc is on it'd be a real shit to get to.^^^ exactly that. Ive had 6mm plate steel crack from minor vibration from stress, so that would be a prime candidate for stress cracks on the T sections. Might not need it but it will always crack at the worst time if you don't.