For bettor or worse, the chop has been done.
One thing I am very unhappy with is the sloppiness of the razor saw, this is one of those times where it pays in the long run to buy quality tools as the blade although tightened as much as I could get it, still had quite a bit of vertical movement. As for the blade being very flexible, I don't know if that is normal or not, but i found that these two factors combined made it very hard to keep on a straight line. Luckily the par I cut off is no longer needed, but if I was doing a cut and shut, I'd revert back to multiple strokes with the Swann Morton, even if it took a long time.
The next step is to make a new "end" for the coach and a panel for the balcony, before moving on to the windows. Looking at the prototype again, there's less work involved than originally envisaged, although i will need to replicate one strip of rivets down the side of a window. If anyone has any suggestions for this, it would be gratefully received.