The sears are not that hard on these and CZ's, easy to file in relation to pivot point arc. No need for a diamond which wont leave file marks that's for hard stuff also no need to take top sear out, l leave it in 2 min job.
Plenty to hold on to in a decent vice just look what your doing, work clean and try often.
Fairly easy Peter if doing for yourself only, just need a section 2 which they pretty much cant refuse. Known convicted drugs dealers serve time and be granted a licence within 3 weeks. If doing an English from scratch 'done right' expect 11 months full time when know what your doing.