Does your Zeus BB have 35x1 printed on the cups? (or 36x24)?

How far did you (gently/hand) screw the ISO left cup in? Did it feel quite snug, or was it loose? I assume the same cup on both sides.

In theory you could salvage two left (adjustable) cups from a pair of ISO bottom brackets which should be fine for all but some of the modern cartridge BBs.

But, first verify you actually have a French BB and not Italian.

Oh, also measure the width of your BB shell to the nearest MM.