Try this:
You'll need a 2" C clamp. turn the backplate up on it's side in your left had with the trap door toward the palm of your hand. put the spring in the hole and place the ball bearing on the spring. take the C clamp and compress the ball and spring until the C clamp is just about tight. you'll need to keep it from getting too tight as you will be sliding the C clamp off as you slide the flipper on. After compressing the ball bearing and spring, place the flipper above the top of the backplate and slide it down in place pushing the C clamp off at the same time. Once in place you can put the pin back in with a tack hammer. It's real easy once ya get used to doing several things at a time.
You'll need a 2" C clamp. turn the backplate up on it's side in your left had with the trap door toward the palm of your hand. put the spring in the hole and place the ball bearing on the spring. take the C clamp and compress the ball and spring until the C clamp is just about tight. you'll need to keep it from getting too tight as you will be sliding the C clamp off as you slide the flipper on. After compressing the ball bearing and spring, place the flipper above the top of the backplate and slide it down in place pushing the C clamp off at the same time. Once in place you can put the pin back in with a tack hammer. It's real easy once ya get used to doing several things at a time.