OK, you have a Corsa Record bottom bracket, or at least that is what was presented. The cups are near carryovers from Super Record, a bottom bracket that also used 3/16" ball bearings. Alloy cups and passed in steel races.
measuring the spindle race spacing won't help much, you are living in the 3/16" ball bearing world unique to Campagnolo.
(they did this for a year in the early 60's too just a point of history)
the spindle notation 68 or 70 is for the width of the BB shell. So, there is your starting place.
Double check the frame, some frames get "faced" to odd dimensions for various reasons.
These spindles were SLIGHTLY asymmetrical, the Pista versions hardly noticeable.
Now, the hard part... locating the correct spindle will be a search... so much so that I would be thinking of looking for a Super Record ti spindle, or spindle with nuts, early took bolts.