To pull the cover/tunnel from around the gear box, do I need to remove the seats?
Normally the answer is yes. Not a difficult job , but it does take a while , and it is a tremendous help to have someone on top while you work underneath. Be prepared that some of the nuts underneath will be seized , so be ready with a hacksaw or a Dremel to cut them loose.
You also need quite bit of space around the car to put the items down as you extract them.