Cinelli stem help?

If I have a 3T stem and want to replace it with a Cinelli quill, do I need to cut down there steerer tube?? If so this seems like a much bigger job than I had anicipated!

Sorry to drop my question onto this thread but its my first post and it won't let me start my own.

any help would be amazing.

No, I don't see a reason why you should cut down the steerer tube.
I thing the shaft is approx the same length. Cinelli is certainly not the longest (quill), so it doesn't bottom out on the reinforcement in the steerer tube.
Both quills will be 22.2 mm diameter.