I have both a 908 and a 457. While I don't have the right precision measuring tools to give you exact dimensions, I can tell you the 457 frame is slightly larger than the 908. Measuring the factory Delrin grips, the 457 grip is wider by about an eighth (inside of the grip; the outside of the magwell) and deeper (front to back) at the base by three-sixteenths. Height is close enough to the same as makes no difference.

Don't know how much this helps, but the factory grip from the 908 will not fit onto the 457. You can get the grip from the 457 on the 908 but it's loose and sloppy. That's just with mine, and may not apply to every unit out there. But it probably does.