Certainly gad I happened upon this thread - Thanks. I learned several things!
My first train at age 5 1/2 was a simple PRR 3 car freight set with the 310 K5. It had the 'Pennsylvania' on the tender. Some years ago I repainted it Brunswick green and it still runs well, albeit quietly. Always liked the Flyer smoke & choo choo but it was several years before I received another K5 that had them. It was a 312 I think...