I am currently in the process of manual swapping my 87 w150. I got the tranny under the truck and went to slide it back further and pulled it from the outputshaft and it popped out. It wont slide back in and when i went to pull the top cover off to look inside it wont come off, i tried putting the shifter on to make sure it was in neutral and it doesn't really go unto any gears. Unsure as to what im supposed to do now.

 

It's very likely that the internal selector rails have become misaligned, jamming the mechanism and preventing the lever from shifting gears. On a 1987 Dodge W150 with a transmission like the New Process NP435, this happens when two gears are engaged simultaneously.