[Yukon Jack]

John is definitely right, you won't know how much you need to modify the driveshafts until the lift is on. A 4" lift usually doesn't require front driveshaft changes but when I did a 4" lift on my 69 K20, it did require changes.

I had to lengthen the front shaft, then when I installed it I had interference and had to have a double cardon joint installed and the shaft had to be shortened. Keep that in mind so you don't have to have yours done twice like I did.

You will also need to make steering modifications with a 6" lift. If you have the closed knuckle Dana 44 you wil need an adjustable drop drag link. Mine is from Skyjacker or Superlift, can't recall which. The raised steering arm that usually is used on an open knuckle Dana 44 won't work on the closed knuckle Dana 44.