Undead Master Wizard is a good fit with an occultist thanks to the necromancy implement and the int focus.
Necroccultist is a nice archetype but probably doesn't add too much to the gestalt part of this build.
I would probably go for panoply savant as an archetype for the extra mental focus and weirdly enough grab the trappings of the warrior panoply for the additional BAB for your summoned undead.
Alternatively you can also go silk channeler, stick to being a full caster, have great spell endurance, an insane amount of HD for your undead and access to pretty much all the spells you might ever need.
