there are 2 bolts that hold the reverse gear in place
one either side of the box halfs (front and rear)
let me go and get some pics of what i mean
if you undo both then it's a bit tricky to get it all back together again

and whatever you do DON'T take the gear selector locater thing apart, it's a right pain in the butt to get back together again, a mistake i learnt to regret