Thanks for the update - news to me. Maybe something scared them off from more modern articulateds.

Perhaps they did not want to spend the money to accommodate bigger equipment. For instance the leased Santa Fe 2-10-4's would not fit on the turntable IIRC in Columbus. They "extended" it with longer rails. Hard for me to picture that and apparently it did not work well.

But the PRR was rich enough to mess with radical stuff like the T-1's and turbines, etc. Seems to me a no-brainer to go with late-generation articulateds like the A which was a multi-purpose engine, not just a drag locomotive like the Y-6.