Mortal magic in the Young Kingdoms seems to be all alchemy and conjuration. Only magical beings like demons have access to other spell-schools. I'd guess you'd need to get rid of all non-conjuration spells for mortal spellcasters. The regular D&D spellcaster classes therefore won't work too well. BTW is Dragon Lords that bad, mechanically? I heard it just ripped bleeding chunks from Stormbringer/Elric!, a good game but one which use the d100 Basic Roleplaying System rules of Runequest & Call of Cthulu.
Incidentally, Young Kingdoms wizards/sorcerers seem more akin to D&D clerics than to D&D wizards; so maybe use the cleric class, but redo the spell list so they only get conjurations, which should reasonably balance them vs fighters & rogues in a lowish-magic environment. The Brew Potion feat would need expansion to allow for the creation of potions of healing, cure disease et al, probably dependent on the user's caster level.
Edit: I have Stormbringer, and frankly for a high-powered game resembling the novels, I think D&D is probably a better rules set than BRP is - in BRP you never get any more hp, it's great for Call of Cthulu but hard to do epic stuff with it. In the novels Elric contends directly with Chaos Lords, even matching blades with Xiombarg at one point.