I'm wondering if the guy who loaded the wagon would know that Preston was on the way to Scotland .................. plenty of people nowadays wouldn't have a clue ! ☹️
As things stand every second Hayes train does, indeed, run via Parks Bridge Jn. ............. Cannon Street has been excommunicated from Hayes - or vice-versa.
While the 158s/159s - whatever the fundamental difference IS - are, indeed carried on one T4 bogie, the P4 obviously differs in some way that makes it powerable. The various Networkers have a variety of P3/T3 variants or BP62/BP52 bogies.