I already said:
jamesinc The screens on these models don't sit inside the headunit, they sit in front of it
Look at the photos in the links, they will answer your questions about what the screen and headunit looks like.
In terms of the electrical side, if you are studying autoelectrical work, you shouldn't have any problems. You will need to cut and splice/crimp/solder wires to adapt the factory wiring to the headunit's connector. The headunit will come with a connector and wiring pigtails, you just need crimps or solder and heatshrink, and a multimeter so you can work out what wire is what. Aftermarket headunits have pretty standard wiring colours, but the factory wiring is not standard colours so you will need to work it out.
Australian 360GLTs were all fuel injected, I don't know if UK ones are the same. Post a photo of the engine bay, it'll be obvious from the photo.