After contacting Sam at Neat Gearboxes, I eventually took the OEM route and got my LSD assembled with a Toyota 4.778 ring & pinion.
I eventually restored my original zenki axle housing, along with new hard lines ready to house the new setup.
This followed with all the parts being removed from the kouki axle and transferred to the new one. The image below shows me organising all the parts in prep for assembly:
Eventually, over the course of a few days, I managed to get this far – the axle housing back in place with its original setup 🙂
Next up will be removing the original oil seals… Thought that it ‘may’ be easier to do with the axle housing on the chassis… Before doing this, I tried to remove the oil seals carefully without any success, so I’m hoping this helps change things a bit.
Doing some research, it appears to be a common issue when removing seals (that it’s not always easy to remove) – especially without risking scoring the finish on the inside. Ideally this should be avoided since the seals might not be able to its job properly in keeping the oil in.
After physically studying the seals, there are a few options that I’m relatively comfortable with doing – destroying them completely with a pair of vice-grips, or use a bearing puller-like mechanism 🙂
The original Toyota SST (09308-00010) is used in the factory manual. It’s an adjustable jaw-type bearing/ oil seal puller that is essentially attached to a mini slide tool:
Once I have some time to revisit the assembly, I’ll see what works for me. The seals are fixed in there pretty good and I’m guessing they are the original ones installed from factory…
Update – 13 Sep 2020
I managed to get the oil seals out by pivoting them inside the axle. I first used a thick wooden stick and a mallet to push one end of the seal in; then using tyre prying tool, pried the other end out (all wrapped in cloth to avoid any marring).
For disc brakes, you want to aim for 2mm when pressing new seals in. It’s a bit challenging to get it sitting flat, but if you have a good set of drivers, you should be good. The areas in black represent a gap between the inner step and the oil seal.
IAD 
Heh, your site had the only picture of that SST 09308-00010. I used the pry bar method to pull out the output shaft seal in my W58, was careful to not mar the sealing surfaces. Had taken off the rear half of the gearbox and hammered the dust cover off to get the room required. Apparently those cheap dedicated oil seal pullers do the job very well.
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Glad to hear the shaft seal came out with no issues. I was thrilled when mine moved despite not having the proper tools at the time. Eventually came across a mini slide tool with attachments similar to the SST – wasn’t cheap but has certainly come in handy 🙂
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