Now got the under carriage rolling on it's wheels in it's rail (u channel).
It runs incredibly smooth and the compensation works exactly as it should so the wheels are in contact with the rail at all times.
I took an extra pic to show the rear frame is not just welded with the triangular gussets. The gussets are an extra to give a little more strength.

https://ibb.co/p0w3S5z
https://ibb.co/Tv4Jf9M
https://ibb.co/WkWF6Tm
https://ibb.co/T8DsqqR

The next step is to gut the range and get the rails screwed into place.
Once that is done, I can get the undercarriage in and build up the rest of it.
More pics to come.