You will definitely need a DC shaft with the lift those slinky’s will give. Per my experience with Slee brand 4” castor plates and 3” of lift the DC shaft worked perfectly. I began going taller and taller up to where I’m at now about 5.5”. As you lift the pinion will rise proportionately keeping the pinion pointed at the transfer case output like it needs to be to run a DC shaft (ideally zero angle between the driveline and front pinion companion flange). The DC shaft will continue to run satisfactorily smooth down the highway but your castor angle will be too little. In my case, with the 4” castor plates and 5”-5.5” lift, my castor was 0.5*. Going to the 6” delta arms has my castor just a bit more than 5* but the relationship between the front pinion and driveline is not “ideal” for a DC shaft. The solution is a part time kit and for more reasons than driveline vibes on a rig you beat on off-road in remote areas. If you are handy with sheet metal work you can cut the fenders to be able to accommodate larger tires on less lift. I can think of a handful of 80 owners running 37”-40” tires on less than 4” of lift but the sheet metal work to do it right (subjective) was very extensive.
This is a game of experimentation for the owner and his rig. What I think is working great for me might not be any good at all in your opinion. Experimentation does cost time and money. Welcome to the game….
job. 
