Sounds like you are going to be missing a lot of versatility since Dread Necro and Truenamer are both small-list casters, and unless the Truenamer is abusing the hell out of consumable recovery utterances and skull talismans, he's going to be pretty much useless at epic levels.
The go-to answer IMO is shadowcraft mage stapled to a cleric. You get full divine casting (which means full BAB due to Divine Power), Heavy armor proficiency if you want it (or you can just trade it out to be a cloistered cleric, AC is a trap by that point anyway unless you can jack your touch AC into the stratosphere), and still get spontaneous access to most of the Arcane Evocation/Conjuration list. Also, divine metamagic for all-day buffs from the arcane list. It's a character that can do almost anything, but usually not all at once, so you can just fill in the party gaps and keep the game going when it stalls out.
- Shadowcraft Mages get the ability to emulate conjuration (summoning or creation) and evocation spells by using [figment]-descriptor illusions (which become [shadow]), similar to the shadow conjuration and shadow evocation spells.
- The maximum level of the spell to be emulated is one lower than the level of the illusion used.
- Heighten Spell allows you to increase the effective level of a spell. Silent Image is allowed as one of the base spells for shadowcraft, so you can just heighten it to the correct level for the spell you actually want.
- Earth Spell allows you to Heighten a spell by one more than you normally could, which overcomes the -1 spell level penalty of shadow evocation/conjuration effects.
Used together, a SCM can effectively spontaneously cast anything shadow evocation/conjuration can create, using any spell slot, while also ignoring material and XP components, AND casting long-duration spells in a standard action.
Early entry into SCM using heighten and divine metamagic to get a 4th level shadow spell early from your shadow domain means you have a LOT of wiggle room, with even casual entry being something like Cleric5/SCM10/Another Prc10
If you use Domain Spontaneity you can spontaneously cast your illusions using any of your spell slots, or you can take a single level of Dweomerkeeper and choose Silent Image as your Mantle spell. DK is MUCH better at it, since DS costs either a turn attempt or a higher spell slot.
Side note: if Dragon Magazine is included in "all 3.5 books", then the War Spells section in #309 has some hilarious options for shadowcraft mages. Stuff like a 25-target/level version of magic missile as a level 2 spell. Normally it costs 600gp in material components, requires a special feat, and takes a full minute to cast, but as a SCM you get to ignore all of that. 1 missile per target is absolute trash in epic, but the SPECTACLE is worth it.