Unfortunately I don't have much time to experiment right now...
The other night I tried to realign cars on the car waggons (because they were not centered) and replaced the VW Golf by red Porsches, but this took me 3 hours of trial and error...
I still haven't figured out how the positionning of goods works out entirely (might be that I was just too tired to think properly).
I also edited all the retiring year values for all the vehicles so it's possible to run an oldtimer train / truck

But I was not successful in re-instating some of the oldest steam engines (pre-1930s), but I think that this might be because the generated map I am playing was started in the 1930s. Hence I guess it's not possible to make this save introduce those engines...
Anyway, as I said I won't have time to experiment in the next days as I will be travelling to the UK (hopefully I can visit the Bluebell Railway while I'm there).
Regards,
JW