The danger in split rims is in assembly. Pull the valve stems from them as you hold them upright facing away from you to let all the air out. Then you can break them down no problem. The problem with split rims is proper seating of the lock ring. If it is not exactly right, the danger is that the lock ring will pop off the rim lip and suddenly fly off under pressure. If they are holding air now, then you should be safe to handle them long enough to deflate them and break them down.
Stand the tire up with the valve on top and the split ring side facing away from you. Being carful to have only your hand in front of the rim, use a valve center remover tool unscrew the valve stem centers and remove them and just let the tire deflate.
Once you deflate the tire, there is ZERO danger from the split ring...with the exception of hitting your finger with the hammer. Break them down by laying the tire flat and stepping on the sidewall or in some severe cases you might need to CAREFULLY align your truck or car and drive over the sidewall being careful to not drive over the rim or ring to break the bead seal. since you are tossing the tires anyway you can also use a chisel to break the bead off the split ring. Once you have the tire bead and split ring separated, you can then find the cut in the ring and while standing on the tire sidewall to hold it down, kick the ring at an angle to "slip" it off the rim lip. You will see how they reassemble and can quickly realize how if they are not exactly right, they can spring off under the sidewall pressure (35-50 psi) with a great deal of force.
You'll find a small cut in the split ring where you can slide it over the rim. This is the area that must be EXACTLY right on reassembly. The disassembly side is no more dangerous than handling a tire on a split rim as far as my experience. It is dangerous, but not impossible.
Once you have them all broken down, sand blast the rims and the split rings and inspect them closely for either out of roundness or corroded areas that may compromise the split ring seating properly.
Most truck tire places will mount your tires on split rims for you. Be careful and work smart around them.
Just out of curiousity, are you sure those 16" rims will clear your tie rod ends ok on the front? Better check them for fit before you invest any time and effort in them.
