IIRC, the Atlas RSD-4/5 had the two closely spaced axles powered, so it would have "B-1" trucks, with the idler axle inboard of the powered axles. If my memory is failing me and it is the two widely spaced axles that were powered, then the truck designation would be "1-B" (idler outboard, i.e. toward the end of the locomotive).
In the 1950-52 "Locomotive Cyclopedia", an ALCo specification sheet for the RSD-4 lists the locomotive type as "0-6-6-0" (Whyte) or "C-C" (A.A.R.). It appears that they had not decided which classification system to go with for diesel-electric locomotives.
The 4-wheel AAR Type B trucks used by ALCo had a wheelbase of 9'-4"; the A-1-A trucks on the RSC-2 had a wheelbase of 10'-6" while the A-1-A trucks on the RSC-3 had a wheelbase of 11'-0"; and the the three-axle Type C truck on the RSD-4 had a wheelbase of 12'-6" total with the axles spaced assymmetrically at 5'-7"/6'-11".
Cheers,