I replaced all my bellows on a Bravo III drive last year, along with quite a few other bits of the transom shield, and I wouldn't class any of it is difficult (I'm no engineer!).
Plenty of info out there, and certainly for the Bravos/Alphas loads of YouTube videos as well.
As the boat's going to be out the water to do it anyway, I'd give it a go, and call an engineer if you do get stuck somewhere.
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