I think it's time to remove the top transmission cover again. On the underside of the cover you will see 3 "sliders" (known as shifter shafts). I think the first and second gear shifter shaft is siezed (it's the middle one). Holding the cover, try to move the shift lever (assuming it's still attached) in 3rd and fourth gears positions watching the movement of the 3rd and 4th speed shifter shaft. That's how the first and second gear shifter shaft should move. Try tunking (tapping with a hammer) on the middle shifter shaft to see if it will move. If it doesn't move it's siezed and your task will be soaking it with PB blaster or the like until such time it starts to move after a few taps back and forth. BE SURE your fingers are not in the path of these shifting shafts when you are trying to move them. Yeah! I'm real sure of that.
Good luck.
