I'm thinking of ordering some 3x3x9s and modding one of them into a cubic 3x3x6. If I can swap out the outer layers from a C4U 3x3x5, it will make the mod job a little easier easier.

Thanks.

That, my good sir, is an amazing idea. just putting that out there.

But also maybe order these puzzles, try it to see if they fit... then if they don't you end up with two very good puzzles. Win win situation

the 3x3x9 is compatible with c4u cuboid puzzles. standard 3x3 pieces fit in just fine too