I did the swap a few years ago. Physically the swap is not that hard. Spacers to lower the engine and transmission (the new Cayman S engine cover might take the spacers place now).
One also needs the Bentley book to see both wiring diagrams. There are some sensors that changed, so wiring changes while relatively simple, are needed. This new engine also has the variable lift solenoids, so those need wired to the DME. I think that maybe a dozen pins needs moved.
Vacuum lines are different. I also installed a IPD manifold so which made it probably even more so.
I used my existing fuel rail, so I had to make some adapters to mount to the new engine.
If I remember right there were two different 7.8 DMEs. I believe that the correct one needed was from a 03-04 Boxster / Cayman. I think the later 7.8 had more memory which gave issues in making the DME, immobolizer, and key to handshake. You will have to tow the car to a dealer so that they can flash these to all match one another.
The car ran, but a new flash was needed by Softronic to make everything correct. They did an awesome job of helping me get it exactly the way that I wanted (like removing ALL e-throttle delays).
I also kept the oil / coolant heat exchanger from my 3.2L since it was larger.
I did all work with the engine and transmission on blocks on the garage floor. That way I could ensure the wire lengths and vacuum lines were all factory looking. I installed the engine and transmission into the car together (requires the car to be lifted very high), but I didn't feel like installing them separately.
