Kato released these N Scale 1:160 Kato Union Pacific Steam Locomotives in the past few years, the Big Boy steamer is just released though.  I found a vintage Kadee Caboose for this set as well.  It has Kato couplers in the pockets where the original Rapido couplers (included in the box) used to be.  Details:

The Challenger 4-6-6-4 has a DCC drop-in motor (no sound) decoder installed and it runs at DCC address 03.  Test Run Only

The Big Boy 4-8-8-4 has factory DCC/sound installed and it runs at DCC address 4014 (the cab number). Test Run Only - see video.

See my photos which are always part of my description.  You can try to find these steamers various sales or auctions or just buy my set here for an instant UP modern steam excursion service fix!  Look for my other auctions for more N Scale.  If you buy it all at the same time, I’ll try to combine shipping to save you money.