Engine mount problems aside, I did manage a bit of progress tonight. After one failed attempt to thread my transmission temp sensor into the bung, I gave it another go with the help of my bro. Look below:
The one on the right is the first (err, unsuccessful) attempt - the disc on top of the sensor head is a washer. We originally thought that the we would need to create a seal at the top, but it turns out that the thread is tapered (slightly smaller at the bottom) and will seal up on its own. What happened was that it was so hard to screw the sensor in that we did realise how close we were to the bottom of the thread. So when the head of the sensor hit the washer, we didnt feel it bite and as we turn a bit more we ended up shearing off the top of the sensor
The one on the left is the good one - I was keen for one more half turn, but my bro was a bit more gun-shy after the first try. We can always tighten it up a bit more if it does leak a bit (not likely). Just have to change the transmission fluid now so that I can swap the bungs out and then I just will have to connect the sensor and all done. Easy peasy. Got some Royal Purple sitting in the garage, so will give that a try this time around. Then just have to get my DIN triple gauge holder sorted