i was given a britpart electronic ignition kit (£15 new! mini specific ones are a rip-off

and i had a quick look, and the trigger (black ring) slides over a tinyest fraction, and sort of engages on the spindle, as it you cant turn it round on the "square" part of it, but it wont go on any further, can i find a way of fitting this by shaving down the insides slightly to get it to fit?