In this design R1 and R2 are replaced by variable resistors (potentiometers or volume controls). the 10k pot replaces R1 and the 1meg pot replaces R2.  You will probably want to run these pots externally so you can adjust the flash rate, and strobe effect from outside the case.

I soldered the 10k pot wire into the R1 holes. 

A diode is required to get the proper strobe effect in this circuit, it is wired parallel to the 1 meg pot.  For simplicity, I put the diode in the R2 holes, and soldered the 1 meg pot to the diode as shown.  You can certainly solder the pot lines closer to the diode body to make this a cleaner connection.  I err on the side of caution when soldering to diodes do to thier sensitivity to heat.