Yeah the heat&coldstones used to be equippable in the ammo slot on live back in classic eq. You didn't get the 3ac in that slot but did get the vision upgrade. Sadly I have yet to find anything concrete to back me up and is probably considered a bug/exploit anyways.

Gnome or Erudite.

The Heatstone has to be worn on the neck, but the Coldstone (Ultravision) can be stuck in the ammo slot, which you will otherwise never use on a Mage. It's basically just like racial Ultravision once you summon it and equip it. It never fades and you don't have to sacrifice an item slot for it. They're also very nice to summon and pass around to your group and will especially be appreciated with the recent darkness changes.

Coldstone goes in ammo slot