Wog, I suspect that one of the vendors you're considering is Tombstone.
I ordered a set of grips from him earlier this year and sent a tracing of the factory grips for the same reason that Dino mentioned. I'm very happy with the end product - a faux ivory set. I had to do a bit of finish sanding, which I had expected, to fit them to the backstrap, but it was all of maybe half an hour's work.
As far as a good fit out of the box, I think that the chances of that are about zero. You're going to have to do some sanding because not only are there differences from manufacturer to manufacturer, but within the product line itself there is a pretty significant lack of consistency. But that should not dissuade you. As long as you send a tracing of your existing frame (or grips), you should get a set that is pretty easy to finish up.
Well we don't rent pigs and I figure it's better to say it right out front because a man that does like to rent pigs is... he's hard to stop - Gus McCrae