I have had good luck in converting adventures for use with BRP. The B adventures are really good for that since you are supposed to fill in the monsters yourself.
For BRP characters, I tended to use Magic World and their systems. But, one could make a magic system similar to D&D's spell system. Because they took it right from Jack Vance's spell system in dying earth. You memorize the spell and in casting it, the magic causes you to forget it, and you have to re-memorize to re-cast. So you can "learn" spells as a slot. You could have a "Magic Spell" skill which gives you a certain number of slots at you hit certain percentages, gated by your intelligence since it is rote memorization. FIguring POW into it for any saving throws or conflict to cause the spell to affect others ?