Unless your centre muffler is "cactus", it's a waste of time, and may render your vehicle unroadworthy, depending on your laws, the droning noise inside the vehicle will send you nuts on a long drive and all this for no, nill, nada, nought performance gain, but by all means give it a go if you must.
Law of physics, "percieved performance increases proportionally to the amount of noise emitted from exhaust".
All I can recall for sure is the bolts are 8mm dia, maybe 60mm long, but not absolutely sure about length, 3 bolts per flange, and that is on my 300Tdi.
Here at LandyZone we have plenty of very knowledgable members so if you have any questions about your Land Rover or just want to connect with other Landy owners, you're in the right place.