One thing to note is that the original didn't use an LED & LDR, but used a Vactrol labeled MCD527. I'm not quite sure what color LED and LDR range you should use. I would start with try a red LED and socket the LDR and try different ones to get a good range. If you were to try a vactrol maybe a NSL32 or VTL5C3 which have bee used on many different optical compressors.
Don't forget if you're using an LED & LDR to cover them in shrink wrap to block out any light and increase their efficiency and effect.
Layout 1: Based on the Schematic in the Request Section