Servos were available,on the bulkhead, between pedal and master cyl as I remember. Rail got the blame, real problem was thinking that if you threw oil at one side of a rotating shaft, the cam, some would still be there half a turn later! If oil had been directed into the follower/cam lobe contact area, things would have been betterNo servo to apply pressure to the pads, better with shoes at least they would self assist into the drum.
Think the rail would block and leave the cam running dry .........