I viewed your post Paul with interest. When I removed the sending unit from my Touring, it fell apart, and for the life of me I couldn't see what was supposed to hold it all together..
Whilst my s/unit differs slightly from yours (3 wires and a guide post), until I saw your post I did not realise there was a 2nd nut at the bottom. In case anyone has a s/unit similar to mine, the filter screen can be removed revealing the bottom nut, or, would have done if mine had a nut there (hence the unit falling apart). No clue how he nut came off, and disappeared off the face of the earth, as the screen was still on the bottom of the cylindrical tube.
Re-assembling it with the addition of the guide post is going to be a bugger I'm sure.
unit as it came out of tank
inside face
outside face (screen attaches to this face)