1968 a833 1-2 gear stuck

I have an a833 that I just had rebuilt. I put it in the car, and while hooking up the shifter I noticed the 1-2 gear finger will not budge. Reverse will move and 3-4 will click once. I tried moving 1-2 in both positions of the 3-4 finger and reverse is definitely disengaged, but no movement at all on 1-2.
I have read online that what has likely happened is the shifter balls are not in the correct detent position. My question is if this is true, can I loosen the cover and free it up? I really do not want to pull this beast out again if possible.
Thanks in advance for the help.