Custom Fat Chance with a 24" rear wheel.  The chain stays still measure 17.25" so the small rear wheel was not designed to shorten the rear of the bike as was done with some of the trials bikes of the same era.   The smaller rear wheel was for more clearance over the top tube.  This was still back when a 21" frame was still considered a normal medium size so it was difficult to find smaller bikes.  It appears as if most of the parts were chosen to fit a woman better, smaller brake levers, shorter stem, smaller rear wheel and sloping top tube. 

From Wendyll @ Fat City

"....after seeing the photo, it is one of very few that were built as prototypes and inspired by our Sales Manager at that time -- Christie Lawyer -- who is a fabulous gal."

This bike was made for Claudia Nix ,who along with husband Mike, owns  Liberty Bikes, in Asheville, NC.