Ok I've finished cleaning up the tool, well as much as I'm going to as it's only a tool

Knocked the top off as suggested by Andy ..

Milled a 10mm tool slot

Drilled three holes for the tool clamping screws, M4 in this case but having done it they seem a tad on the small side so I'd suggest M5.
Then I needed to match the keyway slot on the main part to the swinging section.
Rather than fuss around measuring and then getting it wrong

I did it this way ... lined up the cutter to the main body slot and then pushed the swining section gently by hand into the rotating cutter.

Once I had the slot started I did it properly


Bang on, rather unsurprisingly

I then cut a key from some 12mm round stock, won't bore you with those pic's

All the bits now made it's time to give it a go ...
Please bear in mid the HSS threading tool is not at it's best as it needs resharpening and it's overhanging far too much. Also the swinging tool holder is set over at an angle due to the angle the HSS has been ground at. Even so it worked really well.
I will invest in a new tungsten cutter for this tool after the commercial period.
A 1.5mm pitch at 20mm dia. Not the best picture in the world, sorry. It did come out OK.

Here's a better one, 2.5mm pitch on the same bar ...

Now it's going to be hard to convey just how well this tool works and how much easier it makes cutting threads compared to the "proper" way of doing it.
With no winding out and back in again, no threading dial to watch out for and no engaging/dis-engaging the lead screw, this really is a simple way of threading.
If you have a little time to spare then this is one tool that will gain that spare time back again, and then some, in due coarse.
Here are some more pictures after I cleaned it up a little.




You may have noticed that I didn't use a bronze bush as Bogs did. Not being a high speed device I gathered something simpler would suffice.
Also note the front of the swinging too lholder overhangs the main body in an attempt to help keep swarf away.
You may have also noted that the keyway has stuck itself in the swinging part and not the main base section. This is not by design, that's where it chose to be

I shall probably alter this with some Locktite ...

Credits & acknowledgements:
Mike Cox: for the original concept
Andyf: for bringing this to our attention on this board
John/Bogs: for building and proving the first prototype