Characters are the most important part of a game, so the greatest attention will be given to them. In RuneQuest, there are no arbitrary character classes. Furthermore, the concept of an overall "level" does not exist. Characters must be converted on a case-by-case basis. Fortunately, it can be done in a rational manner.
Converting Multi-Class and Dual Class characters poses no special problem. Simply convert the abilities of the character as noted below.
The AD&D Characteristics of Str, Con, and Dex map directly to RuneQuest characteristics of the same name, for the most part. That is, an AD&D Con of 14 is a RuneQuest CON of 14. The only exception is that damned AD&D percetile Str. If a character has percentile Str of 18/01-18/75, he has a RuneQuest STR of 19. Str 18/76-18/00 is RuneQuest STR of 20. Add two to all AD&D Str scores of 19+ to get the RuneQuest Str.
AD&D Wisdom becomes RuneQuest POW. AD&D Charisma becomes RuneQuest APP.
AD&D Int has a different mapping ratio, summarized in the table below:
AD&D RuneQuest
Int. INT
3-4 8
5-6 9
7 10
8 11
9 12
10-11 13
12 14
13 15
14 16
15-16 17
17-18 18
Derive RuneQuest SIZ from the weight of the character, using the chart at the end of the the "Game System" chapter in RuneQuest.
Discard AD&D hit points, saving throws, etc. Calculate RuneQuest hit points, fatigue, etc. according to the RuneQuest rules. Remember to calculate the skill category modifiers.
RuneQuest has no arbitrary, and stupid, limits on "character classes". You want to wear armor and cast magic? No problem--armor is heavy and encumbrance subtracts from your chance of succeeding. Your priest wants to swing a sword? Okay, spend the time, effort, and money to learn how. This freedom is within the game rules of RuneQuest. You can keep limits of any kind in your campaign. Maybe all religions have a taboo on sharp weapons except for the religion of the War God, who requires sharp weapons. Maybe the sorcerers' Guild has a bylaw prohibiting the use of armor as "unfit for our dignity". Thus, a sorcerer could wear armor, but risks getting tossed out of the Guild (and having a court injunction against practicing magic) for doing so. The point is that RuneQuest is sufficiently "balanced" without the arbitrary restrictions of AD&D.
The first thing to convert is combat skill. Unlike AD&D, RuneQuest does not have a general skill for all combat. Each weapon must be learned separately. To convert weapon skills over, apply the following method to weapons that the character actually has AD&D proficiency in only.
Subtract the "skill THAC0" of the character (THAC0 plus any "to hit" bonuses for weapon specialization but without bonuses for Str, Dex, or magic) from 20. Multiply this by three and add to thirty. This is the character's base RuneQuest Attack and Parry skill with that weapon. Characters eligible to use shields also get this as their Parry skill with a shield. Add the Manipulation category modifier to each Attack and the Agility category modifier to each Parry to determine the final numbers.
For Rogue skills or any other skill expressed as a percentile, simply put the base percentile, unmodified by Dex or race, by the corresponding RuneQuest skill.
Non-Weapon Proficiencies are ridiculously inflated in AD&D. Too much emphasis is placed upon the governing characteristic and too little upon actual learning. Thus, multiply the d20 roll that a character has in a Non- Weapon Proficiency by 1.5 to determine the character's base RuneQuest score in the corresponding skill.
A character has 50% in his native language and 30% in every other language. If you have been daft enough to permit "demihumans" to have a fistful of languages without expending proficiency slots live with it.