From his description, he is not shortening the case, nor changing the neck size. Based on his fuller description in his second post (would have been useful the first time around to stop all the red herrings charging around), he is concerned that the overall case length might increase.
From the sounds of the proposed wildcat, he simply needs to be able to trim all to a common length once sized down and fireformed. Any number of handheld trimmers will accomplish that.
The only secondary question is whether or not outside neck turning, or an inside neck ream, would be required due to the neck being a bit longer and using some of the old shoulder. In my experience, this should not be a problem, but he will only know once he makes a couple of cases and fireforms them. I personally use a Forster outside neck turner when I need to remove brass from the neck.