Well just put new springs on the Jeep and the front DS is too short.
So i gott lenghten the old one. Done it before.
I have about 6" of travel in the slip yoke should i measure for the slip to be in the center of the splines or allow for more down travel than up?
from full droop to at rest there is about 2.5" of difference in the yoke to yoke distance.
i have an RTI ramp in the yard should i put it on there and measure it that way?

 

If full droop is 2.5, I would make the driveshaft so that it has 3" in extension travel. The issue is how much is the difference from full droop to full compression, I don't think you are going to have enough to keep it from Bottoming out or hyper-extending itself. Put it on the ramp!