one month or so ago, I lucked onto a 1988 GMC C3500 trk that I am just tickeled to have. Cab is really decent and needs a few things here and there but for what I give for the trk I don't mind a bit!!  

I got the 454 running and am very pleased with the way its running  but still have to prove the transmission AND after talking to the registered owner he tells me the tranny is sound. He also assurred me the trk is not stolen or in a divorce problem,,he just lost the title and did not want to look for it,,SO I'm game to apply for that replacement title.

  The latest issue is I had to disassemble the steering column to replace the Turn Signal Assy that had fell apart, Anyway, there must be a part missing as the 1/4" pot metal PIN that locks the steering wheel does not move up into the btm of the steering wheel that keeps the steering wheel from turning,,,ya'll still with me,,,?

 I have disassembled it several times and iSOMETHING just aint right!!!

 Does anyone have a manual that covers this year trk or know who carries the manual that shows these details? 

  THANKS for any help.

That missing piece is a linkage that rides on the lock cylinder apparatus pushing that pin into the perforated ring that locks the steering wheel. It is probably still available new from a dealer as they broke pretty easily at times with rough treatment of the lock cylinder.

That die cast housing you reference that holds the lock cylinder, and turn signal switch is called the "Mast Jacket". While you have it apart replace the roller bearing and the nylon sleeve that is in there also which supports the steering column shaft. At the minimum pack the bearing with grease.