I think there is a seam weld at the bottom of the top part of the cylinder (where the pins go into the sides) which joins the top to the cylinder. I don't think you meant this, but perhaps the inside end of the piston rod is threaded so it could be unthreaded from the piston and pulled out, but how would you get the piston to stay still while you unscrewed the rod?Your correct the seal will not go over the bolt eye, I wonder if the cylinder was threaded? how else would they have gotten the piston into the barrel.....