I have some plastic forceps, I wouldn’t want to grip the valve with stainless ones without heat-shrink or something on the tips to protect the valve stems. That said, I’ve used tiny cable-ties to do the job. You may find you have to rock the emgine back or forwards a little to slide the rockers across, as they can catch on the next cam lobe. Careful removing the spring clips, they’re a classic ‘pingphuckit’, which is the sound heard if they disappear across the workshop.
Make sure the clips go back in with one washer either side, the washers tend to stick together with oil after being pushed over by the rocker.
Check out ‘ducatitech’ on youtube, Chris from CA Cycleworks has done some excellent videos on shimming 2v motors.
https://youtu.be/dIj3nSJGPZw
https://youtu.be/3WQY1MRlmH4
You should be fine with the airbox in place.
Make sure you turn the engine slowly by hand twice by hand afterwards to make sure everything’s right.