I sometimes wonder why folks don't just leave the UO8 crankset/bb alone, I've seen many cases where the bb was still ok, still in good adjustment(!), yet one or both of the cotters having been destroyed by attempt(s) at removal.

The original cups, spindle (and cotters!) were of good quality and amply hardened, so where possible I recommend simply lubing the bb externally, using either thick oil dripped in or a good blast from an aerosol lithium grease can.

Adjustment of the bb is easily accomplished with the left arm in place as well, if that's even needed(?).

For actually removing the cotters, one needs to be prepared to use a propane torch, heating the "hub" of the crankarm to the point of oil smoke issuing from this area. A cotter press is helpful, but not necessary, and as far as securing the cotters, one should alternate nut tightening with hammer blows to the head of the cotter until no more nut rotation is wanting to happen.

One last thing is that chainrings can be trued in place, usually starting with blows to the three bolts using a 3# hammer and a thick wooden dowel. From there, an adjustable wrench can straighten any bent teeth and further correct any minor waves in the chainrings.

These cranks can be re-tapped for modern pedals, and the chainrings can be found in 52-42t, 52-40t and 52-36t combinations.

Editing here, just now seeing 3alarmer's post:
The fixed cup tends never to come loose as installed from the factory, so best to leave it be.
<<<<Don't remove the fixed cup unless you can assuredly re-install it to a very high level of torque!>>>>
And yes, for damaged cotters, drilling from the head side working up to a 3/16" drill bit really helps allow the cotter to come out. One needs to center the drill so that it doesn't run into the hardened surface of the bb spindle flat, which would tend to destroy the cutting edges but won't even faze the spindle itself.
Any replacement cotter will unfortunately be of lesser material hardness than the French original parts, so doubly emphasizing here that it fit properly (filed as needed!) and be installed "heavily" according to the method I described above.