In the mid to late 80's the 1 ton D 350's didn't come with lock up .Maybe Dodge didn't think they would hold up at the time. My 88 D 350 doesn't have it.Another little bit of info...The 79 Chrysler 300 was the last performance "B" body with the high output E-58 360,, it too didn't have a locking converter 727.
Very few 727's were lockup. I rebuilt a 727 out of a buddies 90 Ram 1 ton with a Cummins and it wasn't even a lockup. From everything I've read they only made them for a couple yrs. around 79-80 give or take a year or two