After ascertaining I have got enough room on Bradgamer to install Trainz, I tried doing it by installing via Steam on Bradgamer and then tried to copy over my sessions but again, navigation displays were missing from them and there were quite a few missing assets.

This is how I got it to work, matching the working Trainz installation on bradspc:

1. Copy the trainz 2019 folder from BradsPC Steam installation to a network backup drive
2. Copy the BradsPC C:\Users\bgmca\AppData\Local\NV3 Games\trs19 folder to a network backup drive
3. On Bradgamer, rename the above folders as *.bak just in case...
4. On Bradgamer, as administrator, run Explorer and copy the Steam installation folder from the network drive to the Steam folder on Bradgamer.
5. As normal user, use Explorer to copy the network drive AppData folder to the apropriate place on Bradgamer.
6. I did a database rebuild but it got stuck and I had to forcefully exit.
7. The second database rebuild went better.
8. Then I did a forced (control) + database rebuild
9. Just for good measure I did a another normal database rebuild.
10. Started the game - AND IT WORKS! A full clone of the BradsPC working installation.