According to my sources, at least 5 D&H RS-3s and 4 units from GB&W were upgraded to 251 engines by Morrison-Knudsen, rather than by the RRs themselves. Although the official term was TE-56, they are more commonly called RS-3Us.
All four of GB&W units survive today. Just one D&H TE-56 runs now- #506 on the Tioga Central. It is still in Bicentennial colors.