Give that @BDub a cigar! For the record: I knew it had to be a 555 when I asked where pin 3 went.
Just a thought: you can use the core to measure the period and duty cycle of pin 3 or you could just figure out the component values and get it close enough for the core to drive. +1 for the opto-isolator that mohit suggested–why risk the core on the $8 motor driver is the way I look at it.
Have fun with it!