Okay, so after a couple of drafts, I have come to the realization that traditional character classes for Shadowrun is problematic at best.
I have decided to go the Stars Without Number route: the three classes are Warrior, Expert, and Magician. Each class will have a number of Training Packages that cover a number of the standard Shadowrun tropes, as well as a "Shadowrunner" custom training packages that lets you pick your skills, but you get less of them.
It's coming together pretty nicely. So far, I've outlined them as follows:
Warrior: Shadowrunner Warrior, Bodyguard, Mercenary, Ganger, Street Samurai, Tribesman
Expert: Shadowrunner Expert, Decker, Detective, Rigger, Infiltrator, Face, Weapons Expert
Magician: Shadowrunner Magician, Combat Mage, Wage Mage, Shaman, Street Mage, Street Shaman
I'm still not sure what to do about Adepts and Technomancers. JB suggested leaving Adepts on the cutting room floor, and I'm not adverse to this. I might also make Adepts a warrior training package. Technomancers I am leaning more and more toward excluding entirely.
I have also compiled a list of skills, keeping the essential Shadowrun stuff and ditching some of the SWN skills that aren't really relevant to a pre-space cyberpunk milieu. I've also added some skills to reflect the presence of magic, since SWN as written has no skills that address things like magical lore.
I am thinking about putting in Background packages a la SWN...perhaps things like Corporate Enclave, Warzone, Tribal Homeland, etc. to show where a character came from prior to embracing the shadows.
I have come up with a few alternate abilities for the Warrior class as well. Instead of Veteran's Luck, a 1st level warrior may opt for these options as well:
*Deadly Accuracy: Reroll one missed attack roll per combat.
*Weapon Specialist: Select either +1 to all attack rolls with ranged or melee combat, or else +2 to attack rolls with a specific class of weapons (sword, pistol, etc.)
*Badass: Roll d10 for hit dice (d12 if troll) and reroll any hit die roll of 1 or 2 when new hit points are determined.
Those are just a few ideas...perhaps warriors can select an additional ability at 5th and 9th level. (Or maybe just one more at 9th)
I have a few ideas for experts, but I haven't put anything on paper yet.
Spirit summoning and banishment will be resolved using a modified version of the D&D Turn Undead table.