A really nice sounding flanger from the famous Electro Harmonix! I remember it had a bright,clear sound and sounded good with acustic intrument. The four op-amps labeled 339 is one chip op-amp,easy to find. One modification to consider is maybe to ad a mixer at the output to better balance dry and effekt signal. The sweep rate pot is antilog. The use of transistors to create zener diodes are quite rare(2n3563) Just connect the collector with the base and you are in silicon heaven!
I you have +12 volt DC you can omit the voltage regulator in this circuit!