NEW  PLAN...

I have removed the Disco box because:

• The alloy adapter is too heavy for the flexplate - Caused the flexplate to work loose
• The Torque converter is not suited to the diesel engine characteristics giving excessive slip at maximum engine torque (TC stalls at 3000 rpm)
• The torque converter is not capable of transferring all the engine's torque to the gearbox, causing increased heating under normal conditions. (Max Torque transfer is 235 Nm @ 3000rpm)
• Lockup in 4th gear = 90 Km/h before lock-up

In defense of the box, the box is great but the torque converter cannot be replaced with an up-rated unit as ZF only make TC's per application as opposed to a whole range..

SO WHAT NOW ?

I have  fitted a Chev 700R4 box with the following characteristics:

• Way over rated for the DV8 engine (300Hp standard - upgradable to 600Hp)
•  TC Stalls at 900 rpm
• Max torque transfer is way over 500 Nm
• Lock-up in 2nd, 3rd or 4th. - Makes mountain towing a breeze 
• Gear ratios are better than ZF box  3.06, 2.5, 1.00, 0.7

This gearbox is the ideal option for such a conversion, they are ideally suited to each other and the torque converter is perfect. The combination pulls like a train with minimal slip. Gear changes are very comfortable  and cruising is really great.

The very low 3.06 1st gear is brilliant for off-roading and when low range is selected it is unstoppable.

The Gearbox was obtained from All-O-Matic in Booysens Johannesburg, they supplied a fully rebuilt box with a new diesel torque converter, kick down cable and dipstick and tube for around R 11 000. 

The adapter was made by Chris Mod in Hartebeespoort. He does a sterling job using steel tubing and plates.

The trick with the adapter is to move the LT230 transfer box backwards and rotate it downwards so the propshaft clears the valve body on the auto box, as a result, the whole combination lands up 75 mm longer than the original gearbox and transfer box combination. The auto sump needs to be cut and welded to make space for the propshaft. Newer model prop shafts have much more clearance than the older models.

The lower floor of the Range Rover needed to be cut out a bit to make space for the hand brake drum. At this spot, there is a reinforcing type tube under the body, part if this tube needed to be cut away.

The low range and dif lock levers need modification as do the gearbox mountings.

The box needs a huge oil cooler to run cool, but at the same time it can take the punishment without sweat.

I would recommend that only a 700R4 or NV 4500 box be used in a conversion, as any other boxes will have severe dis-advantages. A common option is the Turbo 350, the little brother to the 700R4 - good cheap box but only has 3 speeds and 3rd is 1:1.

The box works really well, changes soon and smoothly when going calm, but if you plant the accelerator, it pulls really strongly and changes at the right spot with sharp firm shifts. 

NEW

I have re-wired the lock-up of the gearbox, so now I can latch it in lockup in 2n, 3rd or 4th. Wow ! What a difference, it now drives like a manual / automatic in one.

Pulls off like an auto, then, after changing into 2nd, it locks up and chugs on strongly, then into 3rd and locks immediately all the way to 4th, engine revs never go above 1000 rpm - real fuel saver.

OLD PLAN

I used a Land Rover Discovery 4 speed automatic with it's LT230 transfer box. 
The auto box manufacturer is ZF model 4hp22 (FTC6099)

The gearbox ratios are

Transfer box ratio is standard Disco 1: 1.193 and
Differential ratios are standard coil sprung rover 3.54 :1

Gear shift lever came from a BMW 535i Automatic (Same basic gearbox as in the Disco)