[swissarmychainsaw]

I think you are right on that; which means my comments were WRONG!

For the life of me I cannot find a center link for the older generation of trucks.

I would say this though:
* I would assume that your 1991 Sub (front end) is the same as the older generations, Meaning the center link and steering set up should be the same from 1973-1991.
(this is an assumption to TEST mind you)
* I would assume that 3/4Ton and 1/2Ton steering set ups are different.

The good thing for you is that Junk Yard these days are very well organized AND this part is likely not in high demand, so it should not be very hard to find.

Sorry I could not be more helpful on this... someone here will know.
Nick