That bracket appears to follow the bottom of the hull. The bracket in this case is “stepped up”.Take your questions to FB - Everything Boston Whaler. Several there have the same boat/hulls.
I have a 17’ with Whaler drive in my shop that is stock and she has 25” motors. If you go 30” when you need 25 ”’s you will regret it.
I can give you stock measurements.
Having done a custom Armstrong bracket on a 32’ Whaler I can tell you it worked perfectly with 25” shafts.
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I don't have too many profile pics, here is one. i'll see if i can get the shop to send me another today. you can see the bracket steps up from the bottom contour of the hull by quite a few inches.Post another photo showing the side profile of the transom and Whaler drive heights.