The lever that goes out to the back of the set is focus. The small one further back is for Picture Centring.
http://www.oldtellys.co.uk/otindex.html and select Monochrome Tubes. There's a diagram half way down. You should be able to see the control here. Watch the screen and tweak. There are permanent magnets controlled here and they sometimes slip, so whip the tube neck parts off (carefully!!) and have a look.
The gratings - do a full IF/RF Alignment and see if this improves it. Then check any caps you haven't changed.
Cheers,
Steve P