Won't know if the cog is splined until I start attempting a tear-down, and I'd like to know where I'm going first, but there IS something under the larger "lockring" (that one has 3 notches) which may be a snapring or circlip. The rest of it sure doesn't look like a stack of spacers, it appears to be solid and the end with the smaller (2 *shallow* notches) lockring has what seems to be a dust seal and the hub cone is flush with that dust seal (so looks impossible to get a cone wrench on it). The 2-notch ring sure looks like you'd use a FW remover and not a lockring spanner, and it sure doesn't look like a typical Uniglide or Hyperglide diameter cassette.