(1956, June Allyson, Jack Lemmon)

“In a remake of It Happened One Night , Allyson and Lemmon ride on a Greyhound Scenicruiser….several minutes of footage.” (thanks Bruce Korusek)
Allyson escapes from her father, who has kidnapped her after she ran away to get married. She travels by Greyhound when Lemmon boards he joins her on the back seat, and this takes up the first part of the movie:

The bus in question is a Greyhound GM PD4501 Scenicruiser. It carries fleetname K485, but this appears to have been applied for the movie, since I haven't been able to trace it. It's first seen parked next to K1931, a 1953 GM PD4104:

Footage of the Scenicruiser reversing gives some idea of its size compared to the GM PD4151 K315 parked next to it:

There's plenty of footage of the Scenicruiser in action:

On arrival at this bus station, Allyson transfers to another Scenicruiser, K2253, a 1955 example, heading for New Orleans, but as she disembarks from 'K485' there's an interesting view of the driver's seat in relation to the seats behind and the seats upstairs:


K2253 is stopped by a closed road, and it's at this point in the film that Lemmon and Allyson continue their adventures across country: