Got the body mounts today, and they work perfectly. The Impreza and Focus bodies fit great now. I think any of the newer 257 mm wheelbase bodies should work!
You can check here to see what chassis a body is designed for. http://www.tamiya.com/english/rc/rcitem/parts/rc11.htm
If it is listed as fitting TA01, TA02, TA03, TA04, FF01, FF02, TL01, or TB01 then it should fit the FF01 chassis if you buy the TL01 body mounts. Just stay away from any of the short wheelbase bodies (ones that have an S is the chassis name, e.g. TA03RS), or any of the wide bodies like the TA02W or "TB01 Long Sus".