I think the subject of thieves in the OSR may soon surpass alignment in the amount of words written. Personally, I just used a thief class that made saving throws (modified by ability score bonuses/penalties) to perform his skills - kind of, save or fail to climb the wall idea. It was simple and worked for the group. Later, I got to thinking about a S&W thief class that gets a flat bonus to some of the existing "X in 6" skill checks in the game, i.e. finding secret doors, listening at doors, surprise, chance to notice a trap, etc. That gives you a thief that lives within the framework of the game, and is simply a bit better than the other PCs at the non-combat side of the equation. Then I thought that you could make each thief stand out by letting him specialize in one skill, say surprise, using the saving throw mechanic with that one skill. I was thinking in terms of the classic caper movies, where the boss assembles a team to rob a bank - you have the greatest safe cracker, greatest get-away car driver, etc. So, each thief would be generally good at slipping through a dungeon's non-combat defenses, and would eventually become one of the best in the world at his specialized skill. Just a thought.
Big monsters should create a nice, dramatic fight-to-the-finish in games, but they often fall flat. The problem, I think, might be that they're surrounded, and with all attacks focused on the one monster, their life expectancy isn't necessarily much more than every other beastie encountered on an adventure. One answer could be to let the monster cause random damage (1d6, 2d6) to everyone within 10 to 20 feet of it, every round. This would represent the problem of fighting a really massive monster that is thrashing around and generally causing collateral damage to everything nearby. Again, just a thought.
Al Nofi's CIC on the Strategy Page is one of my favorite reads. In the latest edition I found this quote:
"During the fifteenth century it was common for German mercenary companies to have a special officer named the “Booty Master,” charged with assessing the value of and overseeing the division of loot." - Al NofiSo, the Old School adventure party can now add a "Booty Master" to the "Mapper" and "Caller". I like it.