This has always been a favorite engine of mine; both in looks and because, at a time when others were buying/building 2-8-4s and other forms of "Super Power", the Pennsy went with a 2-wheeled trailing truck design which proved to be most effective. Need proof? Just read pages 240 and 241 of "Set Up Running" by John Orr; that'll tell you all you need to know.
With this in mind, I'm wondering anyone has ever taken a couple of K5s and merged them into an M1? I would think that it would make for an awesome piece of motive power...you'd just need to make sure to allow for that looong wheel base.
Mark in Oregon