Clark, Spicer and New Process were built for GM application. They came in both direct and overdrive 5th. Since your truck is not original the only way to see what clutch you have is to take it apart. A 5speed will not weigh a whole lot more than a 4 speed. Why do you want a 5 speed. If you want to go faster you will need a 5 speed OD. Top gear in a direct 5 speed is the same as a 4 speed.
