Use a plumber's tubing cutter to shorten the 30/06 cases. Anneal. Resize. Trim to length with case trimmer.
There are lots of case trimmers available, from inexpensive Lee to the excellent Wilson. All of them are good for removing a small amount of neck brass.
Over the years I have converted lots of 30/06 to 7mm Mauser, 8mm Mauser, 7.65 Argentine, 308 Winchester and 7.7 Arisaka using RCBS dies, a tubing cutter and a Wilson case trimmer.