A while back I was going to run Dark Sun (AD&D 2E) using the Legend/Runequest rules. It's not exactly the same as Magic World, but might be of some help.
Combat Style Skill Value
(20-THAC0) * 5 + 50 = Combat Style Value
Magic Skill Value
(Level-1) * 5 + 50 = Magic Skill Value
SIZ Value
T = 1, S = 1-5 (3), M = 5-25 (15), L = 25-49 (37), H = 49-73 (61), G = 73+ (91)
CON Value
For NPCs just use CON value on a 1:1 ratio.
For monsters use HD * 9 – SIZ = CON
OTHER SKILLS
For non-combat/magic skills, just assign an appropriate value for the skill based on the skill value competency levels given on page 43 of the Legend core rule book. (Alternatively see Competence Bands for Runequest or Bryan Maloney's Converting AD&D Campaigns to RuneQuest.)