"Arf, she said." 75Vette, I like your taste in females.
Sorry. Back to the topic.
As I recall things, Lew Horton's 3" round butt N frames were inspired by well publicized custom snubs. There were no round butt N frames so people laid round butt K frame stocks on their N frame, traced around them, then filed off metal below the level of the side plate. A very nice $10 set of gun show N targets was rasped down and sanded. Many gun rag articles described them as converted to K frame round butt. Lew Horton jumped on the bandwagon with adds which probably never actually claimed K frame stocks fit.
Over the years a few rubber and plastic grip manufactures claimed their grips fit both N and K frames. Most used compromise dimensions. One of Crimson Trace's laser models included a space filler for the top of K frame back straps. The OP wrote he found rubber K frame grips that fit. He must have found one of the compromise grips.
P.S. Yes, after finding no guns worth buying I used to bring back very nice $5 or $10 Target stocks from most gun shows as souvenirs.
P.P.S. timichael, You posted while I typed. I owned a Lew Horton 3" 24 during the 1980s. Is my memory that bad or have you not experimented swapping stocks?