B/X Class: Human

 The OSE Advanced Fantasy Player's Tome has a racial class both for elves and half-elves. By doubling the difference between elves and half-elves, we must surely be able to deduce the human class that they forgot to put in all the books. For instance, an elf's maximum level is 10, a half-elf's is 12, and therefore a human's is 14. ezpz.

Human

Requirements: none
Prime Requisite: INT and STR
HD: 1d6
Maximum level: 14
Armour: Any, including shields
Weapons: Any
Languages: Alignment, Common

XP: as thief
Attack: as fighter
Save: as half-elf, -1 at 13 and -1 at 14.
Attack: as fighter
Spells: Memorize a 1st-level spell at 3, 5, and 13. Memorize a 2nd-level spell at 7 and 9. Memorize a third-level spell at 11.

Using Magic Items: may use items that can be used by arcane spellcasters.

Detect Secret Doors: 2-in-6 chance of success when searching.

Infravision: 60 feet.

After Reaching 9th Level: may build a barony as a fighter.

After completing this experiment, I have to note there were a few points I had to fudge. There was no way to extrapolate from the attribute requirements, and the resulting class would have leveled up even faster than a thief. The saves were fudged as well, since they were identical for the elf and half-elf but didn't go high enough.

The resulting class is obviously a little off. For one thing, it's much stronger than the fighter and levels more quickly. For another, there's still too much of the elf in it. If you got rid of the infravision this could be a good upgrade to the sometimes maligned B/X fighter, letting them get in on magic item use. I might pitch this as a plucky protagonist of folklore destined for greater things.