Just premiered for the International Jack Benny Society annual convention, and now available to all: a "new" episode of the classic Jack Benny radio show newly penned exclusively for Project Audion by Bob Hope comedy writer Robert L. Mills. Here, Jack and the gang do a send up of the movie "Witness for the Prosecution" - with W. C. Fields in a guest-starring role.    Here's what Mr. Mills said after hearing the final product: "This as near perfection as any living humans could possibly recreate a 75-year-old radio show. You performed miracles producing this and the program will take its place among the best work you've ever done." As Jack would say... "Well!” That's a tribute to the cast and crew. Go ahead - join our virtual studio audience and laugh at the efforts of these talented voice actors...   John Bell in Alabama Pete Lutz in Texas Ken Jeffries in California Carl Thomas in Texas Bob Beaumont in California Angela Young in Florida Harry Middlebrooks in CA Norman Cline in Kentucky Bob Mills wrote the script in LA While back in Texas,  Larry Groebe oversaw the production