If it is the "new style" KL3 (the one that is shaped almost identically like the KL5), then the FM64 beamshaper should fit. (I have not tried it.) I could not guess which beamshaper would work if the KL3 is the old style.
The F70 fits perfectly as well as the FM64, but the F70 is a lot more compact, lighter, and much better looking in my opinion. The F70 is also easier to open and close the diffuser. It pops open as opposed to a mechanical latch.