I don't have any delusions that these rules will get used by anyone else. At best someone may steal a rule twist here or there for their own house rules. Existing posts and links show the general direction, but here is a general outline:
1. Class is distinct from Race (like AD&D)
2. Most, but not all, AD&D races and classes are present. "Humans" are the only race that can be all classes (like AD&D)
3. Ascending AC - mostly to stop players from whining.
4. Experience points gained through accumulation of treasure.
5. Training needed for level advancement.
6. Minimum attributes for class membership, but no bonus XP from high prime requisites.
7. Weapon vs Armor Class (in some form)
8. Modified Saving Throws - the spirit of AD&D, the form of Swords & Wizardry
9. Defenses similar to 4th Edition D&D.
10. Rolls to learn spells, and spells must be memorized/prepared in advance to be cast.
11. Ritual casting - inspired by, but different from, 4th Edition D&D.
12. Skill system - somewhere in between LotFP and 3rd Edition
13. Group Initiative
14. Changes to HP, Fatigue, and Healing
15. Some unification of Experience Point Tables