B Body drive shaft length

1967 Coronet 440 383 with a 727 and a 8.75 rearend.
What should the drive shaft measure from center to center were the u joint's go mine mesure's 51.562?
It seems like my transmission yoke sticks out quite a bit

Push the slip yoke all the way in, measure the U-joints on center, then subtract 1". This is the ideal length.