The basic spellcasting rules I came up with cover a lot of ground, but there are some special cases that require additional work. The first that comes to mind is also one that is going to see heavy use: healing. Anyone who plays a mage in Shadowrun and doesn't take the heal spell earns the instant enmity of the group. After all, manaballs are nice, but everyone knows the mage is there to heal. He's like the Shadowrun cleric, just with more offensive punch.
The heal spell works like any other in Shadowrun, and thus in many ways it'll work just fine in Shadowitz, with one major exception: the target number of the spell is based on the essence of the person being treated. In my system, the target number is going to be based on the method applied, like all other rolls.
This divide of technology vs magic is integral to Shadowrun however; every mechanic in the game that deals with magic has it at odds with technology. The two simply do not mix, so factoring this into my game is essential to preserve the proper feel.
For the moment, my plan is to use a two tier method system when it comes to healing. It makes things a little more complicated, but piggybacks on existing rules, so I'm hoping actual play isn't impacted much.
Okay, so essence in Shadowrun runs from 0-6, with 6 meaning a healthy person without any systemic alterations, and thus easiest to heal. Below 0, you're either dead or a cyberzombie, and I'm not offering cybermancy to my players, so it's not something I need to worry about. That spread is very close to the range of method scores, and the entire time I worked out possible rules for healing, that essence score kept staring at me.
When casting a heal spell, the wizard uses his method to determine successes as normal. However, he can only apply those dice that roll under the target's essence (minimum of 1) to the heal effect. Those that roll over the target's essence but below the mage's method can be applied to drain as normal. The mage cures a number of points equal to the successes applied to the spell, up to the force.
Now, here's where the difference in wounding comes into play. Since each box of damage is a different wound, it's very easy to track what the mage can and cannot treat with magic: he can cast heal once per wound box. The box he selects also sets the drain for the spell. If he doesn't score enough successes to clear the box out, he reduces it by the number of successes instead. So if a mage scored 3 successes on wound box number 6, he'd erase the mark in box 6 and fill in box 3 instead. But if box 3 is filled, the wound would roll up to the first vacant box as normal. If that's wound box 6, well....
This makes the minor wounds significant but not crippling, which I like. Two characters with box 10 filled are both in rough shape and both have the same die penalties, but the one with a lot of lower boxes filled as well is going to suffer mechanically in a different way.