smokin,
I got a blank/raw upper steering column from the factory.
If you do not modify the QR boss and/or the upper fixing ring/bearing (with the grub screw) you will end up with the about 2cm minimum.
As the raw column was even slightly longer and I had to shorten it on a turning machine, also up to about 5cm (+) of additional length compared to original would had been possible from what I remember.
The boss is welded and also bolted/pinned to the column.
A local shop did that for me.
The bolt pattern/circle is the same. However the screws are not M6 but M5. I used reducers from about 6 to 5mm and of the length of the thikness of the steering wheel to cover the resulting space. Not sure, whether this was necessary though, but well... at least it is about the steering wheel, which seemed to me to be somehow important
If you are interested to do the same construction I am happy to send you some more information.
Rocket Man,
indeed there is a seat upholstery which covers the whole one piece standard seat bench.
This was an option at the German Ariel dealer.
I guess, that the thickness is about 5mm only (if at all), which does not sound much but makes a surprisingly big difference in comfort. Its outside is synthetic leather.
The green or blue pad, which you can see on the seat is just a piece of a thin camping mat, which i use to protect the seat/upholstery against little sharp stones, when I jump on the seat to get in or out of my Atom.
It is also a great insulation for cold for back and bottom, just in case