This is a basic how-to on removing the internals from an F16/F20 so you can swap the housings over to allow you to keep your F16 housing.
1 Remove the gear selector turret by removing the four 11mm bolts at the base and giving it a tug and a wiggle.
Disconnecting the gear linkage can make this easier, if you do this make sure you split as in the pic below not by undoing the bolt on the shaft to save you having to reset the selector.
2 Next remove the reverse light switch. This isnt strictly necessary but can make life easier and it just screws out.
3 Undo the ring of 13mm bolts on the end casing of the box. There are two rings of bolts, the inner one is for the 5th gear cover plate and the outer is for the gear cluster. Its the outer one you want. (that blue thing at the bottom is my finger)
Once thats done the gear cluster will simply pull out.
4 Remove both drive shafts. (if your attempting this i take it you know how to remove drive shafts ;D)
5 Now the difficult bit. You need to remove the big diff preload nut (castle nut) These are set by weight at the factory so you need to mark its position and count the number of turns it takes to remove as it needs to be put back in the same place.
Remove the locator which is a 10mm bolt.
Then you need to spin the nut out. Some people use a hammer and chisel but i am not that way inclined so i made this.
Which fits like this and allowed the use of a 30mm spanner.
Castle nut out. These are bugger tight so have your breakfast before you start.
6 Remove the drivers side diff bearing by removing the 5 bolts and prying it out. This takes a lot of prying and some swearing.
7 Once you have that off you remove the bottom diff plate (gearbox sump) Have a bucket as there will be oil in it.
The diff should fall out now so if the box is still in the car don't have your head under the hole.
Thats all of it apart. Both F16 and F20 are the same to dismantle.
Reassembly is just the reverse except for the diff which is covered below
8 The F20 diff is slightly too wide to fit into the F16 housing and catches on the ends
So it get it in the edges of the housing need to be relieved slightly on both sides.
This is done with a sanding disc covered in wax so to stop the dust getting into your gearbox. Give the inside of the box a good clean afterwards, needless to say filings on the inside of the gearbox isn't a good idea.
Pay attention to the setting of the diff preload nut, it doesn't have to be 100% perfect but as close as you can get.
Replace all seals and gaskets. Refill with good quality 75-80W oil.