Yah....the biggest problem will be having the PC's survive the damage dealt to them.
I wouldn't give wizards and sorcs healing spells (I dunno...it seems to kinda ruin the flavor, for me, but, hey, that's just me). There's probably no mechanical reason not to (maybe increase the levels by 1, though), but it does constrain the spells per day they can cast, and the spells known...
I'd just be REALLY liberal with healing potions, and maybe replace the wizard's Scribe Scroll with Brew Healing Potion (like Brew Potion, but healing spells only).
Or just introduce a common plant that acts like a cure X wounds spell, or something.
Though, personally, I wouldn't stop the cleric from preaching in a new world...I'd say, in fact, that the cleric could be the first agent of the god in this world, wanting to establish a toe-hold in this new world. Right now, Bob the Priest is the only one who can hear the voices of Pelor. But, perhaps by preaching the word, Bob can help convert a new flock...it's like going to a world accross the sea or a new culture, and being the first to introduce you god. And, in D&D, this means that the relationship between god and priest is that much more important, when the priest is the only one who knows the god exists.
