Hi Simon,
I think that they are scale length. Marklin are saying that the totla train length is 130.66 cm and the original coaches were 23.5 meter long and the baggage car was 19.68 meters long. so give or take a 1mm in total length it comes out pretty close.
If you are keen on the train, also have a look at the "Matching" Brawa baggage car for it as well.
It is imortant (well in my view anyway) that it is put together in the right order. The coaches themselves ran in pairs, a first and a second with a kitchen between the two coaches. You should have something like 2nd with kitchen, first, first with kitchen, 2nd. It should not be first, first with kitch, 2nd, 2nd with kitchen.
Cheers
John