BE4 gear box re assembly

[Bobo1]

I have taken the gearbox out of my 2006 mk2 to give an inspection/clean. Took van off the road sometime ago to replace rear axle, which is done. Shortly before I was experiencing a really bad grinding noise from the front end when pulling away/low speed. Originally suspected the clutch or release bearing, but both are fine. Gear box seems to be in good shape also (not an expert by any means!), as does the diff, with only light pitting. I have decided to just reassemble and hope for the best, and failing that bite the bullet and take it to a garage.Only problem is I can't get the box to go back together. Can anyone advise me on this? Is there a knack to it, or any tips? Any help greatly appreciated. It seems to me that it is very close, but somehow snagging on the 'selectors'. Excuse my lack of technical terms! Many thanks.