I used a Zeus 2000 freewheel on a series (a short series) of training rides back in the mid-70s. It was brand-new, and I concur, it was a beautifully designed and executed piece of gear.
However! As best I can conclude, this freewheel was intended for use in a single stage, to be tossed or rebuilt with new cogs after one-day's hard riding (if that)...I wore that puppy right out after a couple of hundred miles. My chain started slipping, and I thought "what the....???!!!" I examined the drive train and thought "what are all those little flecks of silver on my nice Regina Oro chain? Why, that's my freewheel, there..."
Great freewheel. An exquisitely designed and built body. It needed harder cogs. The cogs were purpose-made, and nothing else fit, far as I know.
Charles "I ride steel freewheels" Andrews SoCal