What size are Campagnolo Ultra Torque bottom bracket bearings?
I was able to find an answer on the Wheels Manufacturing Page with a bit of Googling.

https://wheelsmfg.com/crankset-tech

Looks like Campy Power and Ultra Torque use a 25mm axle and 6504 size bearings. 

The Ulta Torque crank requires 6504N bearing. I believe the N post-fix means that outer bearing shell has a snap-ring groove into which a retaining clip on the bearing cup fits.

See https://koyo.jtekt.co.jp/en/support/bearing-knowledge/6-3000.html