OK, here is a thought...

What trip have you seen recently, UP, BNSF, etc... steam excursion that hasn't had a diesel in it?

Without installing a lot of electronics, antenna farm, and other goodies onto a steam locomotive, how about just have the diesel take responsibility for the PTC. It is in the consist, up front and could dump the air on the train if need be.

I am not too sure if PTCs GPS antenna (receiving satellite and/or differential signals in particular) need to be at the very, very front of the train to have PTC work correctly. What happens if it is back 100-150 feet from the lead axle? Does it break the PTC system if there is a slight delay between what the GPS location says the locomotive is at and where the lead axles of the steam locomotive takes down a clear signal? I am pretty sure there is wiggle-room built into the system to allow for this.

If UP wanted to, and probably has the capital to do so, they could possibly implement this setup into a baggage car so they wouldn't have to have a diesel in the consist and keep the 'look and feel' of a genuine steam consist. I say this as they already have their PTC Mobile Laboratory (UPP210) out on the rails testing the system...and it is NOT in the lead, it is sandwitched between two locomotives. So this probably already proves my point that it is possible, however I am not 100% certain this is how the testing is done.

Also, there may be a allowance for bypassing PTC if certain speeds are not exceeded, like 50 MPH. I don't know if this an option, just going off what I know about other countries signaling systems that have provisions for steam operations on main lines (Swedish ATC system not needed for steam operations not exceeding a prescribed speed limit).

One thing is for certain, we will see the answer soon one way or another. :)