284 brass is only .134 longer than a 260 but larger diameter. Both factory loads are loaded to the same length. I really enjoy both my 284's with 140 grain accubonds. One is in a long action the other in a short action but I load both cartridges to 2.960 OAL. Wouldn't have to be much shorter to function in a model 7. Build what you want.
If you want the .260 AI to function as designed, i.e. Safely fire .260 parent factory ammo, you must take off a thread to get the proper .004 crush on the parent case.