The answers have been posted. It has to be one of them. The clutch lever has either slipped off the ball, happened to me. Or your spring is off the clutch pedal. And/or your shifter linkage is not set right. Has to be one or a combination of these things.
Hope that helps, I have no photos to post.
Dan

 

If your pedal falls to the floor, then you dont have the linkage hooked up to the release arm correctly. Even if the spring on the linkage or under the dash is off, the springs in the pressure plate will push the pedal back up if the linkage is on. As far as it being in reverse when the shifter is in neutral, you must have a 3 speed and gotten the linkages out of adjustment or the rods on backwards. Did you mess with the adjusters any, or did you just take them off when the transmission was removed?