Rules changes to suit your world...

[monk]

I've been toying with changing the thief HD to d6 as well. It seems to fit better with the "thief" archetype I think of when I play. Perhaps you need to boost the number of xp needed to level up if you give them a higher HD, though. Maybe that would be a fair trade off?

One of the PCs in my campaign is a Bounty Hunter, which we ruled to be: a thief, but with only half his skills, Fighter attack matrix, and d6 HD. It seems to be working fine.

[scadgrad]

Gee, I guess I'm really out on a limb here as I have a substantial number of house rules that are either options from AEC or ported in from RC, 1st ed UA, etc. A substantial number of these are adopted from some of the excellent OSR blogs. A longer discussion of the house rules is HERE. Comments and house rules for the races are on that blog space as well.

ABILITIES: We use a 4d6 method that is probably too complicated if I'm being honest with myself.
HIT DIE: Use the advanced ones in AEC
HP AT FIRST LEVEL: Reroll 1s & 2s for PCs at first level.
SECONDARY SKILLS: Pick 1 or roll 2.
RACE AS CLASS: Dwarf, Elf, or Halfling can use either option. NPCs, hirelings, etc. are always racial class for simplicity.
DEATH AT 0 FOR EVERYONE BUT... Star Players get a chance to hang in there via the Death & Dismemberment
SHIELDS SHALL BE SPLINTERED: Can be used by Star Players.
VARIABLE COMBAT DAMAGE: As per the B/X Companion, p 24, basically, use the weapon you find to be most fluffy, damage is determined by class and weapon size. Everyone loves this rule.
WEAPON SPECIALIZATION: The Fighter Column can spec at 2nd via the 1st ed UA rules and then again at 7th
SET SPEAR & LANCE ABILITY: As per RC all the Fighting Column may do this though no halfling may use the lance attack.
FIGHTER COMBAT OPTIONS: As per RC, kicks in at relatively high level, 12th for most of the Fighting Column, 11th for Elf and Halfling class.
THE FIGHTING COLUMN MAY CLEAVE: Once vs mooks and that's it. Makes fighters moar funz.
20 IS A CRIT FOR STAR PLAYERS: Double damage by rolling the damage dice a 2nd time BEFORE adding any bonuses.
WEAPON SPEC'D DUDES ARE DA BADASS: They crit on 19s when using their FIRST "weapon of choice", because it's fun to crit on 19s.
CONSOLATION ROLLS: Star Players can always get a dramatic advantage when rolling a 1 on the damage dice.
DWARF, ELF & HALFLING CLASS: switch over to the RC level system (and benefits therein) once they achieve a level beyond their LL progression.
HIGHER LEVELS FOR DEMIHUMANS: as per 1st ed UA

Add to these rules, there are a couple of dwarf variants, elf variants, a new race and it's a substantial amount of add ons.

[Thoth Amon]

Using character creation rules from Original Edition Characters.
DEX bonus is "to hit" with all attacks, melee and missile.
Modified the bonus language table very slightly and only characters with an INT of 14+ are literate.
Clerics roll a d6 for damage in combat, modified by weapon. They can use any weapon and wear any armor. Spell failure applies. Clerics also get spells starting at first level.
Magic-users roll a d6 for damage in combat, modified by weapon. They also can use any weapon and wear any armor. Spell failure applies.
Fighters roll a d8 for damage in combat, modified by weapon. At 10th level they can attack twice per round (3 times with bows or javelins).
Healing has been changed slightly and character can go to "negative level" in HP before death.
Weapons apply a bonus or penalty to base damage. Daggers do -1 damage and Battle Axes do +1, for instance. I also severely limited the weapon list.
Armor has been limited to: bronze breastplate, leather, cuirass, greaves, helmet, and shield. A breastplate has an AC of 6, leather of 7, and cuirass of 8. Greaves, helmet, and shield each improve AC by one point.
Weapons, armor, equipment, and money have been lifted from the 2e TSR product, Age of Heroes. My campaign is based on the ancient Mediterranean.

[Black Wyvern]

Sounds pretty cool Thoth Amon! I always liked bronze age adventures. Only ran a couple one offs though never a whole campaign.