well, the new bits arrived and wrapped in an Arrow bow.
Turkishexpress'
DIY article was invaluable to the project, two thumbs up to Turk for the effort and quality of the material.
I can say getting the old system off was a BIATCH!

First, taking the three 10mm nuts off the front header is not as straight forward as it sounds. the lower right bolt is not accessible with a socket so open end wrench and a bazillion turns to get it off. My upper nut came half way up the stud then proceeded to remove the entire stud with it. This must be something from when the front head was replaced. Once everything was unbolted it took me nearly 30 minutes of yanking and pulling and hitting with a mallot, tow doses of WD40 and the use of every swear word I knew before the rear header finally let go of the cat.
Next I removed the exhaust valve servo motor. this came off pretty much as described without removing the rear subframe. Tight quarters indeed getting into rear area. I cut down the housing to just an arm with the two mounting holes for the frame and rear master cylinder reservoir and re-attached. So far so good. I removed the DucEE I bough from ViziTech on ebay to install in place of the motor and - uh oh, the connectors don't match.
OEM on the left, DucEE on the right
I emailed ViziTech and within an hour I had a response asking for photos of the unit they sent and the OEM unit and they would ship out the right one tomorrow.

That's great customer service!
Installing the Arrow pieces was a piece of cake compared to everything so far. Some more WD40 on the pipe ends to aid mating and everything went back together cleanly. Even the stud that came out went back in cleanly.
The only question I still have is with the clamp around the silencer. It seems a little loose, I can still rotate the can and there's a little space between the clamp and the can. I attached the clamp to the supplied mounting brack as shown -
I think I'll pull the clamp together and put both halves on one side of the bracket to see if it will tighten up.
Here it is all put together. I kind of like it without the center stand.

Sounds great, even with the silencer still in. Now I need to take it for a ride and hope the fatducs manage the fueling ok.