Quick Overview
The F16, F18 and F20 gearboxes have interchangeable internals as far as everything will swap except the main bearings and the 5th gear sprokets (as in the gears themselves, the 5th assembly is swappable though)
The F10/F13 and early F15 boxes have an easily removeable Final Drive pinon from the outputshaft, but the F16/18/20 and later F15's have the pinon as PART of the output shaft, so swapping the final drive is a touch more involved as you have to strip all the geats, selectors and synchros off the output shaft and rebuilding.
Large parts of this will also cover the F10/13/15, just the sizes of stuff will be smaller and the output shaft assembly is a little different.

Tools
Rebuilding the cluster is a pretty straight forward job, you do not need any 'special' tools as such, here is a list:
decent internal and external circlip pliers
short and long reach pullers (ideally 12" but 9" will be enough if you dont mind a slight struggle)
snap ring pliers (like these http://www.ebay.co.uk/itm/Trident-to...item27e218a28a )
Hammer, ideally copper or plastic faced so you dont knurl over any splines.
5mm Allen Key
parallel punch approx 3mm (can bodge with small screwdrivers if you feel dirty)
Usual Socket set, will need a deep one for the earth bolt and a deep 25-30mm for pushing bearings back on.

Terms
I dont nessecaraily have the right names for the various bits of the box, so here is what I call stuff and the description:
Cassette : The main plate on the gearbox that holds the shifter mechanisms and two gear shafts
Synchro (or Syncro) : The bronze rings with teeth that sit between the sliders and gears on the output shaft
Slider : The rings with slots in that the selectro forks move to select the gears
Strutt Key : The three little tabs that sit inside the sliders to engage the synchro rings.
D Washer : The little washer that sits on the reverse shaft prior to installing the cassette in the casing. Its got a D shape inside it hence the name.
Pain in the ass C lugs : These are some lovely locating tabs that sit in the shaft to stop it moving and they are just a pest on the 5th gear end.

Lets get on with it
MAKE SURE THE OIL IS DRAINED!!!!
Here is the box that we had rebuild but werent 100% happy with so stripped it again.
[img] [/img]
Remove the selector turret from the top of the gearbox (try to ensure it is in neutral)
[img] [/img]
Remove the reverse switch, 17mm socket/spanner (I think... could be 19mm)
Remove all the bolts from the 5th casing and main cassette, and then with a hammer CAREFULLY tap around the joints to losen them up and then to move the cassette up, there is a locating dowel so this will be stiff.
Slide the cassette out of the housing, making sure to catch the D washer and the magnet should that make a run for it. You will need three hands ideally unless you are removing it vertically.

so now you have your gear cluster/cassette.
[img] [/img]