Those late-40s-early 50s grips are nice and fairly desirable, so hang onto them. Original 1920s grips show up on eBay occasionally, so you might keep a lookout for a pair. If you intend to shoot your M&P, while you are on eBay, you might want to pick up a cheap pair of Hogue or Pachmayr K-frame rubber grips for shooting to preserve the existing grips. Usually they are about $15-$20. I also like the Thai wooden grips on eBay, but they are a little more expensive. Those I've bought fit perfectly and look great.