After the six bolts are removed the top, along with the shift lever should move straight up, regardless of which gear it is in. BUT if it is in neutral it should be easier and easire to line up and get it back together.
After 30 years of sitting there is probable some rust holding the shift forks to the sliding gear. Tap lightly on the lever with a hammer - trying to "rattle" or "shake" some ofthe rust off the forks. It will come straight up.