I can understand why the PRR has piqued your interest. There's so much unique equipment and rolling stock and infrastructure. The Pennsylvania Railroad is also one of the oldest in the US, dating back to about 1840.
I did find these lists in a quick search of one of my go to sites, they are from "the Diesel Shop": https://www.thedieselshop.us/PRR_TBerry-stats.HTML and https://www.thedieselshop.us/PRR_TBerry.HTML
Don't forget that there were shortlines that interchanged with the big roads, they were always good for unique power or paint schemes. As you creep up on the '60s many of the branches were no longer profitable and many big roads got rid of them, I don't know about the PRR off the top of my head. It was a dark time for rail, and I fear we haven't recovered from it.
