I have the same lens, the board needs to be cut to fit the shutter. There's a fellow in Chicago that makes marvelous lens boards for cheap. He's on Ebay. The shutter needs to be fully engaged and the shutter mounting nut should also fit into the lens board hole. Buy a flat metal shutter wrench to tighten the nut down.after all that's in place screw in the rear element.
If you found the shutter loose I would suspect that's where your light strike came from.