Lines West was Lines West of Pittsburgh. The original Pennsylvania RR ran from Philidelphia to PIttsburgh. From Pittsburgh West they made arrangements and then took control of the Pittsburgh Ft Wayne & Chicago which terminated in Allegheny PA, that is now the North Side of the city of Pittburgh across the Allegheny River from Downtown. That line ran to Chicago.
The other line from Pittsburgh was the Panhandle officially something like the PCC& Stl Pittsburgh, Columbus (maybe Cleveland) and St Louis.
The H10 was built for Lines West as mentioned above. But after (or even during) WWII) migrated all over the system. The H8 and H9 were LInes East engines. The biggest difference in the class was that the H8 had inside steam delivery pipes and 25x28 inch cylinders, the H9 had outside steam pipes and 26x28 cylinders, and the H10 had 27x28 inch cylinders. From what I read the boilers and other specs were the same. Over the years some H8 were converted to H9 and some H9 were converted to H10.
The Pennsy Power book, mentions also that a few H10 had trainphones - but no more information.