Since mentioning PINNING fan-clutches, I have been in-undated with *** requesting just how to go about pinning the clutch and what the outcome will be.
Pinning the clutch is a simple matter.
Either drill through only the outer shell, thread the holes 5/16x18, and loctite bolts in the threaded holes (3 or 4 holes).
When you turn in the bolts, you will feel them pushing the clutches together, inside the housing.
Or, drill completely through the whole thing, all the way through, in 3 or 4 places, and install 3/8 grade 8 bolts w/lock-nuts.
Whichever method you choose, make sure all protruding bolts/nuts are clear of all moving parts and can't eat a hole in the radiator.
If you only want this modification in the hot summertime, or are afraid you might screw something up, or your clutch is still okay, go to a mechanic that sees a lot of these trucks and ask him for any junk fan-clutches he may have that fit these engines.
A junk clutch will PIN as well as a good clutch, and last just as long.
If you keep your existing clutch and PIN a junk clutch, you can install the PINNED clutch in summer, and install the un-pinned clutch in the fall/winter/spring, having the best of both worlds.
