I assume you got the calipers and carriers. My recommendation is to rebuild the calipers. It doesn't take long and you don't have to worry about the seals then. Also wire brush the calipers and carrier and paint now if you are going to do that. Use new M5 rotors which are really heavy, like twice the weight of stock. I think the pads are exactly the same. The 315 rotor size just places them further out for more torque.
Next get busy on finding the rear brake upgrade if you have not already done that. That should be a lot easier since more cars had those rear brakes.
I'm really jealous as my last 535 had M5 brakes on both ends and that was a great improvement in stopping power.
Mike Holbrook
Meridian, Idaho
1992 535im, 17", Euro M5 Throwing Stars 8's & 9's, FK-451 235/45s & 255/40s, M5 Sway Bars 25/20, Conforti chip, Lowes Ram Air, glass sunroof