Ah, gotcha. Didn't see anything in the post that referenced you installing the 4L80e. If I recall, some of the late model r/v series had a 4l80e in them. I would look for a 90-91 3500 in the junk yard. If you go here
http://www.gmpartswiki.com/getpage?pageid=56707 you can see the part numbers you need. The RPO for a 4L80E was MT1. The shift rod you need is 15614394, the shift lever is 15629421 and the bracket is 15614398
Hope this helps.