Will the S52 swap require reinforcement of the unibody to compensate for the added torque? Or will just a strut brace add enough rigidity?
Depends on how safe you want to play it, my coupe had stress cracks in the body running from the diff mount all the way in under the rear seats + the diff mount itself had shattered where the bushing gets bolted, and that's with the original 3.0. With a S52 alone, without turbo, I'd definitely go for the e28 rear subframe and diff paired with some serious reinforcement of the body. Add a turbo and I wouldn't personally want to drive it without a cage (for my own safety), not to mention brakes, steering, suspension, etc that would also have to be upgraded to really get anything out of the turbo setup except for just beeing cool.
With that said, I'd love to have a S52 turbo coupe
Mostly for the technical challenge to create it, but there's no way to do that legally over here..