[FERNSEH]

That old Advance signal generator has been in service for more than forty years and is still spot on for calibration, it's good enough for aligning radios and most TVs.
Tried to attach the CRT to the mask, it's just not going to happen, so my next idea is to install the trimmed up mask in the cabinet and the chassis mounted CRT will then butt against the mask.
Attachment shows the mask test fitted in the cabinet.

DFWB.