Well it's in.
But it is not the discovery box I was originally was going to use. On deeper inspection that box had the wear of something that had driven around the world several times and really need a rebuild.

I sourced another LT230 box, this time a low mileage 1.1.222 transfer box which the serial number prefix 41D shows it was from a TD5 Discovery2 around 2002 as it has the difflock mechanism fitted (but yet unused on the D2).  Later models had the difflock gubbins totally removed.

To make this box suitable for the use on my Tdi defender a coupel of things need to be swapped with items from the old box.
Firstly the hi/low linkage arm is different so swapping the complete selector housing is a quick and easy solution.
The front prop-shaft coupling flange is larger so that need to come off and replaced with the defenders. That involves fixing a locking bar across the flange using the prop bolt fixings that stops it rotating as a breaker bar is used to undo big nut with 30mm socket.

There is no speedo pickup on this transfer box because the D2 gained speed info from the ABS system. The case has a casting dip where the hole would be. Drilling/machining that hole to take a speedo pickup would be pointless because the rear output shaft hasn?t got the gear ring fitted to drive the pickup. When removing the rearshaft end housing it comes away complete with the shaft. This make it easy to swap with the defender?s housing (and shaft).

As for fitting, I strapped it and as I pulled it upwards a few inch at a time from inside the truck, my assistant placed gravel sacks underneath to support it. Once at a suitable height it was easy to lift and slide into place.

The motorway drive is much smoother now, low revs and quite. It is possible to talk to passenger without shouting and repeating whilst cruising at 70mph.

For my reference:

Serial : 41D906137G
LABEL SAYS 1:1.211

Input gear is 135mm long with 38 teeth with part number: FTC4850
The input gear bearing are FRC5564.