my rack is a seat post mount; no legs. don't most modern (last 10-15 years) racks have a hole at the very rear for mounting a light or reflector? as you can see, mine doesn't have legs, but there is a hole at the top rear for mounting an L bracket underneath, which came with the light. the headlight is a blackburn and i bought it the same time as the taillight, but can't remember whether the rear is a blackburn. and before anyone goes off about 'blinkies' i'll tell you right now a) it works great in fog; i parked it and walked a loong way back to determine it's effectiveness, and b) the random flashing mode is definitely an eye attractor.
use your imagination. it will please you.