I'm going to this event, it's a good day out, most of the routes are centred on Liverpool South Parkway-City Centre. The Pier Head has changed so much since the old Bus Station closed in the early 90s, some of the busses will stop on Mann Island as well.
It's been moved from it's traditional day[3rd Sunday in September]as the Liverpool Marathon is normally run then, with disruption in the City Centre.
BTW theres an heritage bus event on Sunday at Heaton Park in Manchester.