CSX MT-6 Slug
The Pennsylvania Railroad was the major domestic customer for the Alco
RSD-12 roadswitcher,
and after serving with Penn Central the survivors were absorbed into Conrail's
MT-6 slug program in the late 1970s, alongside RSD-15s. A decade later.
they lost part of their Alco heritage when they were given EMD trucks.
The MT-6 fleet was split in 1999, and ten years later CSX #1006 was
still in active service, heading westbound on the former P&LE out
of Pittsburgh,
behind SD38-2S #2443, a former L&N SD40-2
de-rated
for use as a slug master unit.

References:
Eric Neubauer, Ken Goslett "EMD's SD38 and Conrail's MT-6 slugs"
Railroad Model Craftsman, March 1992 p.64-70 numerous
photos & HO scale drawings
Other CSX Locomotives: