Ermm... I would check that you put the cable from the gear selector into the side of the transmission correctly. AT least on the 87, there is a cablet htat goes from the gear shift lever assembly, down into the (i believe) driver side of teh transmission casing. I'm not completely sure how it's held in, but I would definately check that. It can also be off inside the gear shift assembly, it is held on with a big circlip. Check that that is ok. I wouldn't say it is owrking right due to the truck not starting in antyhign but park or neutral, because that may be something in the assembly itself, not in the transmission. (i'm not completely sure of that last point).
I know this thread is old but maybe you haven't figured it out yet.