put a spanner on the nut and a ratchet+socket on the bolt, turn one or both anti-clockwise (as you face them)
if it is really tight, get someone else to hold the spanner on the nut and then put all your strength into the bolt wth the ratchet.
im doing mine in the morning!
Have you got a big vice clamp on a workbench?
If you can get it out clamp it and undo it.
What thats a stupid design! do you have to take the part labeled "8" out?
Is it the defo the gearbox banging, I had something similar, turned out it was the exhaust collecting the subframe lol