I have split the cases of my '52 K. The bike is a real basket case and presents a new problem every day, mostly due to my ignorance of the K model.
The cases are split because it wouldn't shift. I could shift from 1st to neutral and back but that was all.
When actually opening the cases, needles fell out from the bearings of the clutch and right side main bearing. I have carefully gathered the needles up but I can imagine there is a trick to putting the needles in place and not knocking them loose when reassembling the cases. The last few inches of closing the cases won't allow me to see what is going on with the needles.
The only resource I have is a '59 sportster manual and maybe that is inadequate. I have the K model parts book with exploded views.
My plan is to clean up the light surface rust, replace the transmission springs and go back together.
I welcome any tips you might have to keep me out of trouble.