Check out Sky Manufacturing for a pre-crumble zone frame RSK. I'm lookin to sell my 3" kit for the 92+ frames so I can get the other one.
The RSK helps with ride quality because having the shackle on the rear of the leaf spring allows it to move in the same direction as the vehicle's travel. Basically, when the spring compresses, the shackle moves rearward instead of having to fight it's way forward.
Deciding on welding is entirely up to you. Most people do because the majority of kits are made for the 92+ frames that are boxed and would also need the crumple zones reinforced. My plan for my pre-92 frames was to cut frame horns off junkyard trucks and fit them inside the existing frame horns so they could be bolted in to make the boxing, then bolt the kit in.