1970 Road Runner drive shaft

[3rd1970rr]

So, I just ordered a new Dana from Strange Engineering for my 70 Road Runner that has an 8 3/4. Does anyone know the difference in lengths of the drive shafts? Figure since the one I have is fairly new, I'll take it in to have it shorted.

 

[66Satellite47]

My factory service manual says 50.39" for the 9 3/4 axle. 51.50 for the 8 3/4 axle.