I'm not an engineer - but I noticed all the designs of planing boats with livewells place the livewells on the section of the boat that is still in contact with the water when on plane & I so called a manufacture (Lowe) and their service rep told me any weight that is lifted out of the water applies extra stress on the transom & throughout the hull which will over time causes flexing especially in aluminum boats which will result in rivets leaking or could lead to welds cracking (depending on boat design) especially at the base of the transom.
So what I took away from the conversation was that you want the majority of the weight in the boat to be born on the section that is in contact with the water while on plane.
You shouldn't be sitting on a swivel pedestal seat while a boat is under power - apparently swivel seats designed to be used when under power from the manufacturer are all required to have a locking mechanism. But that's a safety measure & not related to your question about the livewell placement, in CT it will get you a visit from the marine patrol and a ticket to commemorate the meeting...