68mm shell would be used with either Swiss or FR as well as for ISO/BSC. You might find the threading stamped on one of the cups, if it's on the fixed cup it will be hard to read unless you remove the crank. French specs will be something like "35 x 1" and Swiss might in include an "S" (if you're lucky) so "35 x 1-S". ISO/BSC will read "1.37 x 24". If it says nothing then the only way to tell may be to remove the crank and the cups then check with a thread gauge or use marked cups as a test. Swiss is the same as FR but the fixed cup is LH threaded (FR is RH threaded on both cups). Either Swiss or FR threading was used in Swiss frames, I am not sure which (or both) that Cilo used in the era your frame may be from, but if you have either it would be a strong clue.