I just bought a 92 Century 4 door with the manual front seat, meaning the seat has a lever to slide it forward and back, but no lever for recline. The problem is that the seat back is at about 90 degrees from the seat bottom and not very comfortable. Is there a mechanical adjustment to change this seat angle?

Unfortunately there really isn't any way to adjust one of these seats. It may be possible to pull the seat out and loosen the bolts that hold the seat back in place. Reposition the back and retighten the bolts. If that doesn't work you can always go to a wrecking yard and pick up a set of buckets out of another car that will allow you to adjust them to your liking.