Lionel does make 031 curves in FasTrack, they come in 45 and 11.25 degree arcs.
http://www.lionel.com/products...urved-track-6-37103/
and
http://www.lionel.com/products...urved-track-6-81662/
They also make O31 FasTrack switches.
To answer your question about running locos on curves that are smaller than they're designed for, maybe or maybe not. Others here have previously said that it sometimes works and sometimes not.