To anyone doing this in future, this is the only difference to the instructions attached above. Along with no need to remove the non-existent OBD pocket.
Pop out the plastic peg where I’ve pointed out below.
Then pull down on the front. I started on the right and worked my way to the left.
Ridiculously this was the trickiest bit for me. Rest of it was done within the hour!
Despite what I’ve read there’s loads of room back there - maybe the LHD cars are worse. Remove the unit with
T30 bit. Plan where you want the cables to end up before connecting them, looking at the space available. I placed the big block connector behind the OEM unit. Feed the white connector through and have the eng-custom stuck on the front not the back. WiFi nubbin pointing down. All other cables in front/below tied up nicely.
Messy picture but shows the orientation that worked well for me (most of those loose cables aren’t used and end up tied up tidily). Ignore the Velcro - that’s from the previous owner who I assume tried the opposite direction.
Practice on the provided wiring loom! It would have been so much harder if I hadn’t spent a fair bit of time fiddling with it last night.
Purple connection: Notice that there is a tiny little clip on the purple connector that need to be depressed before it can be removed. It is stiff on the oem unit however.
Big block: work the clip and then the lever angles out. The lever need to be fully out for the block to go back in, before clicking firmly back into place.
White connectors: very easy, don’t go entirely in but should make a firm click once in.
You have to be firm pushing the unit back into place as the loom is fat and stiff (teehee) but it will go. Try not to crush anything behind it of course. If it feels stuck it’ll usually be caught on the OBD port. Don’t stick on the eng-custom until the oem unit is in place to make this far easier, but you may want to put on a cable tie loosely ready to tighten after.
I used double sided padded reg plate adhesive pads to attach and they were the perfect size, extremely strong and leaves a couple of mm between the two units for ventilation.