Model 69 with a round butt and 2.5" barrel.
AFAIK, the Model 69 has a round butt*. Once you figure out how to get the barrel back to 2.5" or 3" (for full length ejection), you've got it made.
My duty revolver is a Model 686-6 and came with "square butt" Hogues on it. Since I like the round butt better, I swapped out the squares for rounds. I don't think S&W makes square butt revolvers anymore.
Update. This is done with the 2.75 inch Model 69.