I have an Ofmega cottered bottom bracket which I believe might date from the 1960's or earlier perhaps. I removed it from a no-name frame which had vintage Campagnolo drop-outs. This type was available certainly during the 1960's, if not earlier - having BREV CAMPAGNOLO in small lettering across the top of the axle slot and also with axle adjusters.
The lockring has the [small] letters O F M E G A, each in a circle, spaced around it's perimeter. The lefthand cup incorporates a hexagonal "nut" for installing / removal and the righthand cup has three slots around the outer edge of the quite prominent flange. The axle is assymetrical for a crank / double chainring. Ball-races are fitted.
I have read that this style of Ofmega bottom bracket will only accommodate Ofmega cranks.
Does anyone know anything about old Ofmega bottom brackets and their compatability with any double cottered crankset please ? Did Ofmega manufacture their own brand cottered double crankset in the 1960's ?

I think they were compatible with Campagnolo, but cottered cranks at the time may have been actually more universally compatible. The size of the cotter was the kicker in most setups. If you used the wrong size, even if you drove it in pretty well, it would start to loosen up in a few miles and put a hitch in your pedaling giddyup.

IIRC, Ofmega and Magistroni were either the same company or at least closely associated. Magistroni cottered cranks were common on Italian bikes of that era.