Make the Kohler rail system even stronger
Especially for that behemoth cast iron, "clips" do not cut it. Here is a Kohler undermount kit:
http://www.us.kohler.com/onlinecatalog/detail.jsp?item=5808102&retail=false
If you click the "designers and installers" tab you can look at the install instructions.
You can Make the Kohler rail system even stronger if you are floating your counter top on a piece of plywood. I would think most people are doing this, since if you are using a cast iron sink, you are probably also spending money on granite or stone. You will notice that these metal rails sit on clips that sit on the horizontal pieces of wood of your sink base cabinet. The load path goes into this horizontal piece of wood, then since its attached to the side of the cabinet, it goes to the side(s) of the cabinet. If you screw the plywood that you are floating your granite on very well to these horizontal pieces that the metal clips sit on, the load path now goes to the plywood mostly, but more importantly, most of the load goes into the sides of the cabinet and not into the horizontal pieces of wood that the clips sit on. Its also better to install the metal rails closer the the outside edge (Left and Right as you are standing in front of your sink) since there will be less wood bending. Also to use regular plywood not particle board which can bend over time.
One other thing to point out is that if you don't have a center support in your base cabinet, you have a shear load on each side of the horizontal pieces of wood of your base cabinet where they meet the side of the cabinet. If you have a center support (the doors hit this when closing). The load of the sink is resting on this pc of wood. I only mention it because transferring the load path to the sides of the cabinet are more important in if you dont have a center support in your sink base cabinet. Screwing the plywood down to the horizontal members is probably only necessary if you dont have a center support, but it only takes a few seconds either way to shoot several screws near each metal clip and along the horizontal member when you are doing an install.
This is only my 2 cents, but I dont think its good practice to attach a cast iron kitchen sink directly to stone. Especially since a large portion of stone is cut away for the sink. If a contractor is worth his salt, he will support the sink by the cabinets in some fashion BEFORE the stone goes in. If you introduce a permanent bending load into stone all the time, thats just less load you can put on top of the countertop or you may get a crack later if something wasnt flat along the counter top. A cast iron sink with dishes and water could weigh up to 300 Lbs.
I hope this helps someone.