Conversions

Based on Old School Essentials at its core, most classic roleplaying material is usable directly with almost no change. With a few additional changes, material from many other places can be used.

Here are a few basic guidelines and suggestions.

OSE, B/X, 1e, 2e, Classic Gaming

Stats can be mapped as follows:
Dexterity <-> Quick, Accurate, Discrete
Strength, Constitution <-> Strong
Intelligence <-> Cunning
Wisdom <-> Resolute
Charisma <-> Persuasive

Take the average of Quick, Accurate, and Discrete to get Dexterity.
Take the average of Strength and Constitution to get Strong.

Spells cost (10 * spell level) XP to be learned as Abilities.
They should cause about 15% (1/6) of their effect in Corruption to the character that uses them.
There shouldn't be any concern about "low level" characters having "high level" spells, as such spells should be extremely rare. NPCs that might know them would be well justified in very difficult to meet requirements (or entire quests) before passing them on as knowledge.

If you'd like to use treasure as XP, offer it as 1XP for every 10gp brought to safety. Alternatively, divide all treasure values by 10 and offer XP for 1gp. Either way, don't include any other method of gaining XP.
Alternatively, you can offer 1XP for every 100gp worth of treasure as an additional method for gaining XP. If a character were to bring 100,000gp to safety, they would have gained 1,000XP. That's 15 abilities and 11 level 5 skills, which would be roughly comparable to a level 7 or 8 character.

Remember that characters in Ravensaga never gain more HP or improve their AC and therefore need to have many more tools than their OSE counterparts in order to have the same level of survivability.

Monster should not require any additional modification beyond updating their stats.