With a bravo drive running thru hull exhaust only. Would it be better to have a exhaust boot to stop air coming through to the prop. Or leave it open ?

There's exhaust outlets at the bottom of the transom assembly and the lower is vented to the outside towards the rear above the cavitation plate, so I don't know if it really would matter

No reason to run the exhaust boot. Neither my AT or Pantera had them.

Exhaust tube instead of a bellows on big block applications.

Mine is a BB with a B1x and it had a Bellows. boat left factory with it this way. its no longer there. I was wondering if I was possibly sucking air in at speed through drive. I saw a bulletin a while ago, but didn't pay any real attention to it