I have the same kit on my 2.5.
I believe the Renix era trucks used a two piece speedo cable for the factory setup. You'll have to use the magnet kit on your truck.
I was happy I didn't have to use that. I thought it was a bad idea too, especially since they want you to put the magnet on the D.S., which is going to be moving up and down, so it couldn't possibly always read correctly.
As for the over-rev protection for if you throw in the clutch without turning the cruise off first, I wouldn't rely on it. I tested it a couple times after I installed the kit and it did not work. Either the system's faulty, or the 2.5 just simply does not rev quick enough for it to think of it as a problem.