If you're running HD or lifted springs, you won't/don't need the self leveler....
Only the 110" CSW models (and RR classics) have them so they could run softer springs for better passenger comfort, yet still retain load carrying capability. A normal 110" just runs heavier duty springs.
You can remove just the leveler unit, and keep the existing A frame ball joint mounting (has an extra section on it) or fit a 90/110 (non CSW)/Disco ball joint mounting. The first option is easiest!!
For the MOT... you could just clean it

... a spray can of brake cleaner is ideal. Do it just before you leave for the MOT and it should stay clean - then sort it out when you get chance.
Ian