If you put some 40-48 drums on F-1 backing plates you'd need to push REALLY hard on the pedal to get it to stop. The 40-48 brakes are 12", the F-1 are 11". I don't know about putting early brakes on an F-1 rear axle. I'd think at the least you'd have to redrill the backing plate mounting bolts. But maybe the offset distance is the same?