The final 97 locomotives had piston valves mounted outboard of the cylinders, instead of inbound as previously built, giving the cylinder assemblies an outward cant at the top, rather than inward.

All B6sa and B6sb locomotives were retrofitted with power reverse to make the frequent back-and-forth of switching quicker and easier.

The last PRR locomotive in active service was #5244, leased to Union Transportation of New Egypt, New Jersey until July 1959.

It has a larger tender, from a 2-8-0 Consolidation, but it is intact, albeit in poor condition.

In 2019–2020, it was donated to the Historic Red Clay Valley Inc., and the locomotive remains on a siding near Mt.