I have found the tree pairs of adjusting screws to correct (adjust) the typing alignment and I understand that I should start by sorting the lowercase alignment. Originally I was going to ask how to remove the mask but having frightened myself by reading ‘TypewriterGuy’s’ account of how to build the 3 Bank. I think there is no mask as such and that the outer casing forms an integral part of the build.
I wanted to have easier access to the lock nuts on the adjusting screws as my spanners  cannot effectively reach them. If there is no easier solution I will have to make my own spanner . Has anyone found a commercially available make of spanner that they can recommend as the steel I have access to may not be up to the job?