F16s all share the same selector forks so swapping between them is easy.

If your fitting an F20 cluster its easier to use an F18WR 5th as the selector forks are the same between the

F18 and F20 but not with the F16

If you dont feel confident taking your gearbox apart the please dont start.

This is fairly simple to do but its still the inside of a gearbox 

1- Remove the end cover of the box. This is the inner ring of 11/13mm bolts

2- now looking at the gears you need to:

Remove the two circlips arrowed in GREEN

Remove the two 5.5mm allen bolts that are arrowed in YELLOW

The left hand gear can now be removed by gently prying it from behind with a screwdriver. It is in a few parts so keep hold of it as you pull it off keeping the selector fork with it and being very carefull not to let the two bronze bushes (circled in RED) fall out.

3- Removing the left hand gear requires a puller but it does just slide off once the circlip is removed.

This is what your left with. Be gentle with it and keep it absolutely clean

Removing the F20 one is exactly the same and refitting is the opposite. If your doing this with the box still in the car jack up the passenger side only so you don't loose gear oil.