.......The rebound block spring does have a tendency to want to leap away when replacing it. I found that a simple 1/4 inch wide thin screwdriver if ground so it's got a "V" point on the nose makes a great tool for putting the spring and block back into place. Grind the tip so the point of the V is in the middle and the angle between the sides is fairly open at around 120 to 130 degrees. You want the point to center in the spring but not hold firmly when you push the block back down over the spring retention pin.
This will suddenly make total sense when you have the side cover off the gun and see the workings. .........