That was something I didn't know that they'd wanted it to run with someone else later.
I was thinking from the Pomona group's perspective on that they lost a big draw for the museum and 3985 could have helped to fill the void.
It makes sense, but as I ask my wife when she assumes I already knew something, "Why would someone ask a question if they already had the answer?"

Didn't Pomona gt at least one old Diesel as part of the trade?

They got a Missouri Pacific SD40-2, one of the Rock Island cabooses that Union Pacific funded and then took back around 1980, and a boxcar.

Yes, but none of you could say that the Pomona folks wouldn't have loved to have gotten 3985 once UP decided to get rid of it.
If UP only wanted to give it to someone who'd run it, then that would seriously limit those who would get it.
Besides, we all know what a pain it was getting 4014 across that parking lot now that their museum tracks are so far from any other railroad.

She'd been restored and run so recently, it simply makes more sense to build on what had been accomplished in the past twenty years. I'm fairly sure that if the Challenger had not needed a huge investment of resources, something on par with maintaining the largest steam locomotive ever constructed, they'd have kept her running.

I seem to recall a discussion in Trains magazine at the time 3985 was returned to running condition that the Challenger was considered a more successful design than the Big Boy when the Big Boys were delivered, and that the main claim to fame for the Big Boy was that it the largest (and that may not have been true, as it appears that Lima fudged the weight of the Alleghenies downward). I am not certain of either of these points, I am simply reporting them.

https://www.youtube.com/watch?v=E-rcj3QwxXk "Iowa Interstate manifest PESI (Peoria IL to Silvis IL) rolls by Mossville, Rome and Chillicothe areas late-afternoon Tuesday, February 21, 2023. IAIS 507 and IAIS 719 have 56 cars, including four ex-Amtrak (nee Santa Fe) hi-level cars (PPCX 39914, 39926, 39938, and 39942) shipped from Gateway Rail Services at Madison, Illinois to Railroading Heritage of Midwest America's Silvis, Illinois shop via UP-Peoria-IAIS." David Jordan images and video, from the "Peoria Illinois Railroads Trains & Shortlines" facebook group, used with permission.

So no one told them "Handle On Rear Of Train ONLY"?!?

I wonder if they wanted them on the head end so the crew would remember they were there. Note the green decals on the side doors, which may say "Do Not Hump", also the same bulkhead flats that you mentioned in your post about the ex-Santa Fe hi-level car for AZ. This move was likely the first time hi-level cars have been on that section of the old RI Peoria Branch, although a Santa Fe passenger train detoured on the Rock Island between Joliet and Chillicothe in 1969 and may have had them north of there. There are spots depicted in the video where I stood among 20 ft. tall trees between the rails in 1986 when the line had been shut down from Henry to Peoria for five years.

The green placards say "HOME SHOP FOR REPAIR--DO NOT LOAD". They're such "standard issue" that I still have a pair in emergency reserve from escort duty years ago.

It is certainly possible to temporarily refit passenger cars with heavier draft gear and/or couplers to ease shipping and lower risks of broken couplers or the like; at least one of my clients did that some years ago. And given that we've seen any number of instances where crews in the 21st century utterly lack the reading comprehension to obey "Handle on rear of train only" (though the car shipped to Arizona got lucky in that regard), I would highly recommend it to any passenger rolling stock shippers today if they have access to the right gear.

And remember that the number of hump yards is slowly declining--though I have personally seen crews just about miss "DO NOT HUMP" signs about that big on all sides and ends of a passenger car as it reached the top of the hump.........

The indoor facilities at Silvis are far better for restoration of the Challenger than the outdoor museum in Pomona.

Silvis has a railroad connection -- the display at the Pomona fair grounds is without a connection.

When the Big Boy was exchanged a temporary track was laid across a parking lot to make a connection with the MetroLink trackage.

This might just be me being paranoid. But I've been worried about what might happen if Jim Vena takes the reigns at UP

Why? Is Mr. Vena anti-steam?? Thanks, Ross Rowland

It’s assumed he is anti-PR as he did a lot of stupid anti-PR stuff at CN and he was basically EHH’s second in command.