Hi Dan! I think the only company that makes any versions of the 251 is GasOline (and possibly Propaganda Co.) and they are resin, of course. Sad to say, but true, we will have to wait for the AFV Club's 251 to get a halftrack in plastic.
This is based on the very, very old Bellona plans from the 1960s, and has a number of basic accuracy flaws. It can be largely fixed with a lot of effort, but an easier way (assuming AFV Club actually does release their new 1/48 SdKfz 251 ausf C) is to convert the ausf C back into a B using the front of the Bandai kit for the new nose. There are no really accurate interior drawings available commercially for the ausf A/B, and Tom Jentz reports there are no official German loading plan drawings for the ausf A/B either. I have been working up an interior layout for the basic /1 infantry carrier, and it's the best I can come up with. When the AFV Club '251 ausf C does come along, I'll post an article on converting it to the earlier ausf A/B.
there is a decent chance AFV Club would do the ausf D later. If not, the ausf D body is very easy to scratchbuild, even for those who haven't done it before. it IS a very simple body, and can be built using the ausf C body as a support template for the D body panels. The interior is almost identical to the ausf C, especially the early D models.