A375: Sort of - that is, yes they do stack, but you need two separate Aid Another actions (one to improve your ally's attack, and one to improve their defense) to trigger both items. You therefore need a way to Aid Another as a move action or less (e.g. Swift Aid, which slightly reduces the bonus) to do them both in the same turn. The other limitations of Aid Another apply as well (i.e. only lasts for your ally's next attack or the enemy's next attack respectively, you generally have to be in melee range of an enemy that is in melee range of your ally, you have to hit AC 10 etc.)