Unfortunately, with the 669 you’re stuck with either the factory grips, or Pachmayr rubber grips that have steel inside them. Doesn’t fix the huge blocky feel, IMHO makes it worse.
Best way to fix that problem on a 669 is to shoot too much +P+ through it, crack the frame, and send it back to S&W to fix. If they still have any 6906 frames, they’ll swap it in and only charge you about what you already paid for the gun. But it’ll be really sweet afterwards!
Ask me how I know….
Or take em completely off and wrap it in hockey tape like I do everything else lol.
I carried USPs and P12s for most of my adult life and the boxy grips never bothered me.