I am guessing that if Flak Jackets can be donors for Juliet they can also be donors for Penny. I would go down that route as Flak lenses are still readily available.
I would keep your XX lense safe and if you have the larger Big Taco lenses, keep for the larger lenses like XX and Rome 1.
I would keep your XX lense safe and if you have the larger Big Taco lenses, keep for the larger lenses like XX and Rome 1.