From the size of the fuel tank, I'd actually think that might be a RSC-3 rather than a RSD-3. The RSC has A-1-A trucks, and is for lightweight rail on branchlines, while the RSD has C-C trucks(6 powered axles) and was the Alco equivalent of a SD7 or SD9.
Oh, and for the fellow who said the RS-1 was ugly compared to an S-1, well the RS-1 was just a S-2 on a stretched frame, with a short hood added, the long hood and cab are nearly identical to an S-1.
Oh, and for the fellow who said the RS-1 was ugly compared to an S-1, well the RS-1 was just a S-2 on a stretched frame, with a short hood added, the long hood and cab are nearly identical to an S-1.