Looking to replace the oe metal fuel pump on my Kohler k241s that’s in a old Allis Chalmers 310d tractor with the newer plastic bodied one. Took the old pump out and while pulling from the block the arm lever and pin and spring came out . Are they supposed to? Is there something that keeps it together? Is it possible a piece went into the block? Here is a pic of the old pump

It should be one piece.  
 
The shaft should be slightly pressed in (friction) holding everything together.
 
It appears you have all the parts...

I kinda though something would have been in those round circles to hold the pin in. And looks like it was stamped to hold those from coming out. Idk. If you have the pump together and get it in without it coming apart I don’t see how the arm can fall out because of the clearance. Wish I had a picture of one just like it .