Lift kit swap question.

[99ccsbdually]

I have a 94 k3500 crew long bed with a 6 inch lift but the frame is soft. Yesterday I scored a 99 gmc k3500 crew short bed Dually for cheap. I want to take the lift out of the 94 and put it in the 99 my question is what’s the best way to do this? Completely disassemble then reassemble or leave everything together and unbolt front frame, steering etc and slide it out as a unit?

Has anyone done one other the other? Pros/cons?
The 94 has brand new everything in the suspension so it’s all going to the 99.