Converting 5e players to OSR and AD&D

AD&D is a much better system to convert 5e players to OS D&D than Basic is. B/X is a very minimalist system in which player options are few and advancement is limited, while AD&D shares the same conceits as 5e, 3.5, and Pathfinder, such as the separation of races and classes, unique class features, and a profusion of modifiers to the die rolls of every action. The "power curve" of AD&D characters is also greater than B/X/BECMI, and characters are expected to start out strong and remain strong in order to survive, which is a more natural fit to modern players.

To play AD&D effectively you must create a powerful character at the outset. Race and class are separate so players can create unique character combinations. Races give statistical bonuses to ability scores, so players can choose to optimize for a certain style, and classes grant special abilities and gain extra features as they rise in level (in fact I think every class gains new features upon level advancement except the humble fighter). Multiclassing is an option for nonhuman races, so players can combine them to create their own unique builds.  In AD&D 2e there are no racial class limits, so players can choose to play whatever they want. And if you play AD&D 2e, you get even more customization options in the form of Class Kits and Non-weapon proficiencies, which are the same as skills.

AD&D is a more lethal game than 5e and there is a greater emphasis on the management of resources such as time, money, weight and inventory, more detailed mathematical calculations for performing and resolving actions, and more pressing consequences for player choices. Because almost every action has some dice mechanic and a series of modifiers attached, AD&D rewards system mastery.

If, as a DM, you are attracted to OS D&D because of the lure of heavier consequences and lethality, but want to maintain the number crunchiness and wide array of options from modern RPGs, then AD&D is a better fit for your table. If however, you want a more minimal game where those options don't exist, and players are all better off playing standard Fighting Men and scrapping through a dungeon by the skin of their teeth and their wits alone, then OD&D or B/X/BECMI is a better option.