Hey - that same sh|t happened to me once when I rebuilt my 3.6. To add to the problem mine was a nylon washer that I used as part of my home-built mechanical chain tensioner. It had about the same dimesions.
To further add to the missery my case was oily inside (I did not split it) and the washer got stuck to an inside oily wall. No turning over was helping that situation. It took me four hours to make visual contact and another two to get it finally out. At time I was ready to say "screw it, leave it in there and see what'll happen" or push the entire engine over the cliff. I was so frustrated.
Glad you got yours out and slick tool. I hope you cleaned it before you used it
Ingo