After seeing X4014 Union Pacific Big Boy in person running, part of me likes the idea of a steampunk mini bike. Question is, other than a picture, was such a mini bike actually built?
Other than a homemade steam boiler, I have no idea where one could even source it. I could barely make out what the old article says (reading on a phone is a bit blurry), but it appears to run at 600F and at 450psi...that's a lot of pressure to be near your legs if it were to go boom.
Regardless of any dangers, I'd buy one in a heartbeat.