Filco <-> CM Storm Rapid are incompatible because of internal case dimensions.
I think the filco PCB would probably fit in the Cmstorm case, but the real incompatability comes from having the standoffs in different places.
I am pretty sure the filco TKL is compatible with a PLU-ML-87 case. I'm not sure about the ducky, but I rather doubt it.
If you're willing to modify the internals by clipping the standoffs and re-gluing them, you can probably get it working, though you may run into an issue with the arrowkey-part being slightly differently spaced from the main cluster. If i recall correctly, on the keyboards where the spacing is different, it's usually only a little, so you can probably get it still.
I guess it all depends on how much work you want to put into this project.