HELP! Stuck GB Lifting Arm

Hello everyone!

Ok, so I have a friend with a 75 Mark3 who had to install a new front primary chain sprocket as the original was quite worn. He had to remove the clutch basket to be able to install the primary chain on the new sprocket, so far so good. He calls me to borrow my clutch tool and he manages to get the basket off, clean the plates, install them same order and thread the large cir clip back on, call me come on over adjust the clutch now.
I come over and thread the big slotted bolt till it seats then back it off 1/2-3/4, adjust the handlebar clutch take up and pull in the clutch to verify all is well. NOPE.
The clutch main spring is not deflecting in and out, no movement at all. So I assume the lifting arm in the gear box has dropped, sure enough it looks like it is out of position.
Slacken everything off, even take the clutch cable out of it holder in the gear box.
Put a needle nose pliers on the end of the arm, can wiggle it just a little, very little.
Remove the large slotted clutch adjusting bolt to make sure nothing can be binding anywhere, still can't move the arm, wiggle, curse, wiggle, nothing.
I have not dealt with a stuck arm in probably 40 years so no memory of the cure.
Can you guys help me out, what could be causing it to not be able to move into position?
THANKS

If the arm falls down before you put the clutch nut on and adjust the slack, then the clutch rod wont allow the arm to pass backward into it's correct place, unless you either undo the adjuster nut on the clutch so you can back out the clutch rod, OR take the outer clutch cover off and remove the bolt that holds the arm in the slot in the split end of the shaft.

the easiest thing if you already have the primary cover on is just open the clutch adjuster opening and remove the adjuster screw and nut so the clutch rod can back off. (edited to say that I see you already removed the adjuster nut, so that clutch rod should move)

thanks! The arm just got freed up and now the clutch is adjusted perfectly, thanks again