So, for the time being, I am making my world around D&D 3.5e (as a campaign setting, I suppose). The problem is, the world is very low-fantasy. Most of the base D&D classes use magic one way or another and it really just doesn't fit in the setting. If I got rid of all the magic classes, I would be left with Fighter, Barbarian (which also doesn't fit), Monk (which has no place in the world), and Rogue. I know that there are no-magic variants, but are these even worth playing to most people?
The second thing is: there is no real pantheon or deities, the magic (if there is going to be any) and religion would work much like Lord of the Rings (which is to say, it is not as important as the pantheon in D&D). Magic would not have domains or any such affiliations. It would just be magic. There is a god and (what you could call) deities, but everyone knows of them and respects them in their own way, but again, it's not part of day-to-day life. There is no church or organized religion.
Two questions: Should I just make my own system? If not, how would I go about adapting 3.5e to suit the setting?
EDIT: I am not using any of the standard races. I have created all original races (though, they are mostly just variants of Humans). There are no Elves, Dwarves, Halflings, Half-Elves, Gnomes, Half-Orcs, etc... If you're curious, I have written SOME information down. You can find the races: here. Note: The information on these pages are definitely going to change.