Things are progressing slowly. Problem with teaching is that pupils tend to get in the way of personal projects
and progress can only be made while I am in school.
Managed to machine the stand-offs to go between the wall and the frame. This will allow me to finely tune the parallelism and trueness of the rails once mounted to the wall. Below are pictures of the stand-offs and CAD rendering of how they will be positioned and used. The nuts either side of the frame will allow very fine adjustment and although the whole leveling and truing process is likely to be lengthy, at least I know I can get it right.