So, I've been re-thinking how I'm going to do magic in my conversions/games.
I came across my first spellcaster conversion while doing the Sunless Citadel for a solo play: Belak the Outcast.
Looking at my conversion guidelines, he would have a +4 to his Miracles skills, but what would his starting attribute be?
The answer I came up with is to incorporate a system from D6 Star Wars: Advanced Skills. Now, when converting a Spellcaster, you find their highest spell level able to be cast, and this becomes their advanced skill level. For the example of Belak: he's a 4th level Druid, able to cast 2nd level divine druid spells. So now under the Acumen attribute, he has (A)Nature's Miracles 2D. This (A) skill gets combined with the parent attribute to try and cast spells, so Belak has a 3D+2 Acumen, combined he rolls 5D+2 to cast any spells.
Hopefully this makes sense.
Cleric: Acumen - (A)Divine Miracles
Druid: Acumen - (A)Nature's Miracles
Sorcerer: Charisma - (A)Spontaneous Magic
Wizard: Intellect - (A)Wizardry
I'll probably cook up some additional options for each of them, giving Wizards lower difficulty numbers on spells that they prepare every day, whereas Sorcerers are able to shape their spells using metamagic for less of an increased difficulty. A cleric's deity has to condone the action being undertaken by his cleric.