I remember several posts on this topic around the internet. I seem to remember Ron Volstad saying that the halftrack crew was designed for Dragon's series of sdkfz 250 halftracks, some time before the 251s were planned. So they don't fit well with the 251s. I think what threw people off is that these were released around the same time as the 251 C, and the box art for that kit featured the commander and machine gunner from the figure set.