Good morning, Bill;
EPOI (Ehrenreich Photo-Optical Industries) was an interesting company indeed.
Regarding the ST-450 Stabilizer/Timer, if the timing section is not to your liking, you might consider keeping it around for the voltage stabilizing section on its own. That is probably the main part that is duing the humming, although it may be off key. If this thing is as heavy as I think it is, there is probably a constant voltage transformer inside it. Somewhere on it there should be a label telling you what the current or Watt rating it is supposed to be good for. If this rated amount is more than what the head in the Durst 1200 draws, use it for keeping voltage fluctuations off the head and keeping the light output constant. You can put your new timer in series with the power line going to the head. It sounds like a nice piece of equipment.
Enjoy;
Ralph Javins, Latte Land, Washington