k03 and k03s have the same turbine, the compressor is a bit larger on the k03s.
a k04-001 has a larger turbine than the k03 and k03s but i think the compressor is slightly smaller than the k03s. you would be better off hybriding the k04-001 with a k04-023 compressor but that needs modification of the compressor housing. as said, littco can make the hybrids and he can get the housings made up easy enough.
i went down the easy route and bought a chinese k04-001, but its not a k04-001, it has complete k04 sized internals. simular to the E05 hybrids you hear about. if and when it fails i know i can just get a genuine k04-023 and fit the cartridge into the housings after an overhaul.
i plan to buy WMI kit next then go for a custom map when cash allows..lol