For most of the chase, Ray is driving Ecto-1, while Egon and Winston try to catch/delay the train. However, one attempt shows Egon and *Ray* leaning out of the passenger side of the car. This would have required them to stop the car, change drivers for the attempt, and - since Ray is seen driving after the attempt fails - stop and change again. Since they're trying to catch a train which already has a head start, this seems like an illogical and unlikely waste of time.
As Winston and Peter are walking along the tracks, right before Peter is abducted, Winston briefly appears as Ray in an overhead shot and then correctly turns back into Winston in the next shot.
While on the overpass, preparing to jump onto the train, the long-distance shot mis-colors Ray and Winston's uniforms.
While playing with his toy train in the Firehouse lobby, when he is shown from behind, Peter is briefly wearing his uniform instead of his regular clothes.
Just before he is grabbed by Casey Jones, Peter is mistakenly with Ray instead of Winston in the railroad yard.