At last, a nice, tall and comfortable chopper style backrest that will work with your existing seat. 
 
This full size backrest is designed to mate up perfectly with our sissybars.  Hardware is included and there is also an internal metal plate for sturdiness.  Will only fit bars 1/2-3/4" in diameter.   14.5" tall by 6.5" width.  If you are not purchasing for a Combustion Industries bar; make sure to review dimensions to ensure compatibility.
 
Mounting instructions here.