Another who has to ask "why?". Those Mafacs are the best part of a UO-8. (I rode my UO-8 25 years and into the ground. 22,000 miles in all weather. I think I changed just pads and cables that whole time. And once I put aluminum rims on, they were stoppers. (In its last years, I took it down Juaquim Miller into Oakland many times with no thought of braking power or how old those brakes were.)

I now take sets of Mafac Racers and turn the rears into fronts and equip two bikes with Mafac fronts. I do the opposite with Weinmann or Diacomp center pulls which are stiffer and less powerful. Means front and rear brakes feel very similar and have the same relative braking power. (The same squeeze gets front to (say) half of lock-up/flip and rear to half of skid in back.)

And the cruel (to UO-8 lovers) joke that was true 20 years ago: You want NOS Mafac Racers? $50. Go to any garage sale, But you have to remove and dispose of the attached UO-8.

I have Shimano dual pivots on two bikes. Too much power! Way too easy to have bad things happen in a panic stop. I de-tune them with V-brake levers. (Now I was taught decades ago to be in the drops anytime things got "iffy" - pavement, traffic, other riders - and have large hands so full braking with mismatched levers isn't an issue.)

Ben