I'm not a fan of the "one AC altering item at a time" thing either; as far as I can tell, this was house-ruled in by the devs and does not seem to have any basis in 2E RAW (then again, 2E's defining characteristic is using the RAW as guidelines as opposed to hard and fast rules).
Huh. According to the readme for the tweak pack, in 2E pnp while you could wear multiple AC boosting items, you'd only gain the AC benefit of one of them. Other benefits, like improved saves, from the items would still apply, though. To quote the readme:
"P&P Style: In Pen and Paper AD&D, characters are allowed to wear magical armor with Rings/Cloaks/Amulets of Protection, but only the armor class bonus from one item would apply."
As a 3.5/pf player, the idea of different things adding the same type of bonus (armour bonus, shield bonus, etc) not stacking with each other seems perfectly normal :)