To say the coupes tunnel has been massaged is a nice way of saying it, it has been massaged so far that in one spot they have welded in a patch which is a triangle plate about 150mm long and 30mm wide.
For the position of the engine that is up to you where you make it sit as it depends on what you want from it. The coupe engine sits higher and more forward than the sedan, the sedan was positioned to lower the weight of the engine and put the weight as far back to help with handling and it also allows the radiator to be thicker and taller. The coupe has the radiator mounted under the frame at the front which allows the engine to be mounted forward but as mentioned this puts the weight at the front which wont help the steering.
Here are a couple of photos of the location near the fire wall and radiator.


