I just had a little play around and no, the main outfits don't fit the old style FS...
The old FS have much thicker legs, and the new style t-shirts have sleeves that are quite tightly fitted to the new FS size.
The skirts look like they might be able to fit. The skirt from the FS I bought doesn't really fit together properly though (can't get the two halves to stick together
) so I can't tell 100%
Shoes won't fit again because of the much thinner leg/hoof size.
The head accessories like headbands etc can fit the old FS, but the new FS have much bigger, rounder heads, so the accessories look a little big on the old style.