First timer. 4 speed rebuild issues

Back up the bus guys
That is an overshift alright, ;
1) are the two special long-shoulder bolts in the correct cover-holes? Take a look at your case on the two vertical mounting rails. you will see two counter-bored holes,one on each rail at about the center;to receive the long-shoulder bolts. If someone failed to install them there, then the cover could be misaligned and anything can happen.
2) And while the shifter may attempt to overshift, the internal detent stops in the side cover are supposed to prevent that. So the 70 and older cover have the interlock pin with the two balls and spring.Go take a look at your cover. If you have this early cover, shift the front lever into either gear, then attempt a shift into 2nd.Firstly it should be impossible and secondly, the lever should just perceptibly move.If that is how yours is working, then the problem is not in the cover.But,if you get two gears the pin is missing,and if you get more than a few thou movement, then the pin is too short.The later cover has a roostercomb interlock.They are almost never trouble.
3) Next grab the output shaft, and attempt to move it into the tranny and attempt to yank it out the back. There should be ZERO back and forth movement. If it moves, there is a problem in the bearing or in it's locating system. Be rough with it. ZERO movement is what you are looking for.
4) So once that is also proved ok, then you have to look to the brass rings. If they sit too low on the cone-clutches, then I have seen the struts pop out on the backside, making it impossible to backshift when the assy is spinning. Sometimes after the driveshaft stops turning, then you may, or may not, be able to backshift.
5) If those are ok then you need to look to the geartrain end play. But that almost never needs adjusting.
8) the spring is in no way responsible for this.NO WAY AT ALL.