The first stage is to remove the extra bit of resin casting which you can see sitting next to the body in the picture above. Then I opened up the doors and windows. Unfortunately I slipped with the knife and went clean through the roof but a quick drop of superglue and all was well.
I have added some weight at both ends of the loco as it is very light without this. To disguise the lump of whitemetal in the rear bit I've enclosed it behind some styrene. I'll add a little seat and a brake wheel which along with a driver should be adequate disguise for the mechanism. A cab floor wouldn't go amiss either.