Your timer could probably be converted to 220/240VAC, but don't do it (It would require a change in wiring to the transformer and a different transient suppressor, maybe different caps). Use step-up/down transformers instead. Or isolation relays. It is a little clumsy, but much easier and it will get you printing sooner. As for the 50/60 cycle problem, I'm not sure how the Z6 measured time. When I designed the MetroLux 2, I used the crystal frequency as the timebase. Does the Z6 timer even have true seconds? If the only 'timebase' is from the light intensity, that will not be affected by the 50 cycle power.
As for photo diodes, there are several that can be used. If you are looking at a coldlight, then the IR cutoff filter (light blue) probably doesn't matter. There isn't any near-IR content to Aristo's coldlight spectrum. And if you are getting too much light, have the photodiode look at something less bright or partially cover it. Don't use a photodiode with a lens molded over it. If that is all you can get, then sand the lens flat so it is omni-directional.