Dennis,
I still had no luck looking it up in my database. I looked at all engines with a number of 52, all 2-6-0s, and all "U RR Yut" engines (the way "U de Y" is listed in the database.)
The closest ones are 2-6-0 "Lilly Belle" (don't know the U de Y number) at Magic Kingdom and 2-6-0 number 353 (previously 29) on display in Veracruz, Veracruz, Mexico. Both Baldwin built.
This doesn't mean U de Y #52 doesn't exist; I didn't know about the little Disney-built engines either. But I would think it would be a lot harder to keep as large an engine as this secret for so long.
-James Hefner
Hebrews 10:20a