While Conversion spell is highly inspired and well thought out mechanically, I find it to be missing the point on several angles:
1. A good preacher lets "the words of god" speak for themselves, converting listeners by sheer power of persuasion. A 24-hour ritual (vs. a willing or helpless target) just doesn't paint that picture.
2. It's hard for me to see how an effect that targets an individual and doesn't require an attack roll would also not allow SR.
3. There seem to be too many different ways for achieving the same result. I find it to be an unnecessary complication.
4. I hope that the Chaos/Evil/Good/Law distinction doesn't stand for domains, because the official rules offer some backdoors for gaining domains.

This is how I'd do it:

Enlighten the Infidels
Level: Cleric 5
Components: V, S, F (holy symbol)
Casting Time: 1 round
Range: Close (25 ft. + 5 ft./2 levels)
Target: Target Creature
Duration: Instantaneous
Saving Throw: No
SR: Yes

This spell converts a creature's moral (good vs. evil) or ethical (chaotic vs. lawful) alignment to that of the caster's deity, provided the caster shares alignment with his/her deity.
The spell channels and amplifies the caster's reasoning and persuasiveness vs. the target creature's life experiences and inner conviction, forcing it to confront external (or internal) truths.

One axis is affected per casting, even if the caster has a dual alignment extreme (e.g. LG) or no alignment extreme (N).

To find out if the target is affected or not, make an opposed check between the caster's Diplomacy skill and the target's level (1d20 + HD + Wis-mod) or Sense Motive check (whichever's higher).
If the caster prevails, the creature has a sudden epiphany into the benefits (spiritual, material, or otherwise) of the desired alignment, and immediately changes its alignment appropriately.
If the target prevails, it becomes immune to the spell by that caster, until such time when the caster either gains a level or additional ranks in Diplomacy.

Adopting the new alignment generally (but not necessarily) makes a creature friendly towards you and other similarly-aligned creatures.

As a divination effect this spell simply reveals subjective or objective truths about the cosmos or the target's own nature. Therefore it may influence creatures immune to mind-affecting effects. However, mindless creatures lack all comprehension of morals and ethics and are therefore immune.

Creatures that already possess the desired alignment are immune to this spell.