Open-back factory N-frame target grips fit snuggly on a K/L frame gun, but the grip is "proud to the frame" at the top. A little judicial sanding will convert this N-frame grip to fit a K/L-frame gun.
NT on L.jpg
For closed-back grips, it probably would depend on the grip. I only have a set of Jay Scott N-frame closed-back grips for comparison. These fit tightly on an N-gun.
js on N.jpg
On a L-gun, the fit is
not tight - there's about 3/32 inch wiggle front to back at the top. You can see that the top of the grip does not contact the top rear of the frame as it does on the N-gun.
js on L.jpg
I suppose you could do some "plastic wood" fill-in to make these N-grips fit snuggly on a L-gun, but it probably wouldn't look very good.
I don't know how other makes of closed-back N-grips would fit a L-gun, but there would probably be some degree of modification necessary.
My dollars worth.