Coming to an end.
I never quite got round to fitting the fan to this Pi and to be honest it has been gathering dust over the last few months while I have been using my new Pi Zero. With the arrival of the Pi-SPROG 1, I now need the Pi 3. With the SPROG plugging directly into the GPIO header I may not have space for the Heat-sink, never mind the fan so I will put this project to bed.
If you are interested or curious about model trains and digital command and control please go here for the new project:
Finally if you have been following this project, thank you and I hope it has been useful.