I remember when Radio Shack used to sell the SAD-1024....early 80s.I dunno. Replicating the tone of an early-issue Electric Mistress CAN be done with current-production chips. It requires additional circuitry, to compensate for what came naturally to the Reticon chips but not to the Panasonic chips. But I think of all the owners of well-loved vintage effects who cannot find a replacement delay chip for love or money. To see this lot used for the purpose of new "authenticity", kind of bugs me. If either of my MXR Micro-Flangers went on the fritz, I could probably never bring them back to life. And they're not the only SAD-512-based flangers or choruses out there.
There is no denying that some of the very best flangers EVER used Reticon chips, whether 512-stage or 1024-stage. The reason is that the clock inputs on those chips had very low input capacitance, enabling them to handle very high clock frequencies, necessary to achieve the ultra-short minimum delays needed for dramatic and "chewy" flanging tones. The Panasonic chips have a much higher clock input capacitance, which tends to "de-square" the clock pulses it gets, once they get above 100khz or so. If the clock pulses are nicely buffered, however, the Panasonic chips can be pushed MUCH higher. I've personally seen one get safely pushed up to 1.5mhz. This is why I say the tone of the old Reticon-based flangers can be replicated with even lowly Coolaudio and Beling chips.
I don't wish to be critical of someone honoring a great design. But it starts to feel like someone shooting an elephant, in order to have the ivory to perfectly replicate the keys of a late 1800s Steinway.