I always hope that these posts will help people. If you are building a kit, it's useful to read about potential problems before you encounter them.
Which is why I mention that all did not go well when I first mated the Barclay body to the chassis. It wouldn't sit down properly.
At first I though this was due to the motor hitting the inside of the firebox. Que lots of squinting down the boiler and worrying how I was going to grind the shaft even shorter.
Then I spotted the real problem. The boiler bottom sticks below the footplate and hits a couple of chassis spacers - the ones I've coloured red in the photo.
A few moments with a mini-drill and cutting disk removed the front spacer, and cut a chunk out of the boiler to clear the one by the motor. I had wondered if the front one should sit in the slot in the boiler, but to do that would move the later forward exposing a hole in the footplate and clashing with the motor.
Anyway, all the work is invisible and not the body sits where it should.