A character's armour class in OSRIC will be the same as in S&W (despite the fact that some armour types, such as banded armour, don't exist in S&W) with one exception: A character with no armour using the descending AC system in S&W (AC9) would have an AC of 10 in OSRIC. Other than that, the armour classes resulting from wearing armour are the same. Experience point progressions are quite different, however, so when converting a character to one system or the other, simply keep the character's level the same, and adjust the XP to conform with the new system.