Before you have a frame builder add the couplings to your Nomad Mk II, are you familiar with the concept of a Rinko bike?
The concept is to strip your wheels and fork off a full size bike that was not fitted with racks. And that is larger than the typical airline size case, but it still is small enough for most train travel. Some do that with regular straps to strap it together, some use some specific brackets to hold parts in place.
Not sure if that would meet your needs or not, but before you have the couplers put on your Nomad, you might consider whether or not packing your bike like a Rinko bike would meet your needs.
This is only one example, but if you did an internet search you would find many others.
https://www.renehersecycles.com/how-small-is-a-rinko-bike/I think some with a really small frame might leave the fork in the frame.
I keep both a photo of my headset parts in the right order and orientation on my phone to install the fork quickly without having to think about it, I store the parts on the steerer tube and keep them there with a rubber binder. I also keep a copy of the headset PDF on my phone.
The third attachment, I do not recall where I saw that, but I saved a copy to my hard drive in case I ever wanted to try to ship a bike that way. If I recall correctly, in this example the bike owner had a threaded rod that he put through both wheel hubs inside the skewer holes to hold the two wheels together against the frame, wing nuts on the threaded rod. And he had some DIY wood blocks with elastics to hold his wheels together, you can see them in the photo.
