An S&W Model 64 is not a heavy gun. If I can CC a larger, heavier 4" S&W N-frame or 4" Ruger GP100 on a 31" waist, you can CC your K-frame. I CC'ed a Model 19 and Model 66, both 4" K-frames, like your 64, in a Sparks 200AW or a now-discontinued Eagle Industries IWB rig. I also did, and sometimes still do, CC a 4" Ruger Speed Six in a Milt Sparks PMK holster; a Speed Six is a very near-twin of a Model 64.
These days, I usually CC the same P229 pistols I use for police duty, so the Speed Six is getting a break, but when I no longer have to tote a .40 autoloader at work, I will go back to using the Speed Six, at least some of the time; all-day comfort, especially in that Sparks PMK, and fairly easy to conceal.