The short kit won't work when going from 3 1/2" to 2 7/8".
The short kit is for a 1/4" adjustment.
You should be able to lower the center post from a 3-1/2" shell to a 3" shell, then use the short kit, to get you to 2-7/8".
You'll have to readjust your crimp station no matter how you do it.