I re-form cases for my .357 Herrett from .30-30's, and it's quite a bit more involved.
Actually, I'd just use the .260 dies. They'll probably work fine as is. Remove the expander button from the .260 decapper and polish it REALLY well with oiled emery cloth. Lube the inside of the case necks with a neck brush and lightly lube the expander ball and necks with some Rooster CFL (case forming lube). It is available from Midway. There are other lubes. None work as well.
If the decapper is smooth and the ball and neck well lubed, the necks typically open right up if you use slow, easy pressure.
Go to Varmint Al's site
http://www.varmintal.com/index.htm and you'll find everything you need to know about annealing. People make a big deal out of this, but it's really easy.
You most likely won't have to turn the necks. They may be thin anyway because you're stretching the brass from .243 to .260.
As a note, I'd still try Remington brass. There was an extensive article in
Handloader an issue or two ago. Remington has as good of quality control as Norma and Lapua. At one time, Remington must have had some issues with soft brass, but this seems to have been corrected.