Since I am clarifying things and I can't sleep I'll also say that the 518/46RH in the diesel application was non lockup. There were gas versions in both lockup and non lockup. The lockup for the diesel didn't happen until 94 with the 47RH. The VSS was additionally used in these applications for lockup control independent of O/D.

It is also possible to convert the non lockup 518 to a lockup. I did it to my 92 and it totally changed the characteristics of the truck. Less RPM, less heat, quieter cabin, better fuel mileage and excellent highway passing power. It's the best modification that I've made to this truck. The only thing I need to work out is an independent control of the lockup. I just tied it to the O/D so they work together but with a switch so I can turn off the lockup if needed.