The Accucraft BR 45 has a wide, but short chimney and in order to fit a Summerlands Chuffer, the chimney need to have a simple extension fitted. You will need a piece of 11.8mm external diameter brass tube from K&S. Cut this to 40mm and clean up the cut ind with a fine file.
This will be pushed into the lower part of the chimney to extend into the smokebox. Test it for fit and if too loose, then squeeze one end in the vice to make it a little bit oval. If too tight, make a saw cut using a razor saw, for the full length of the tube.
The exhaust is off centre on this loco and so may be difficult to unscrew. If so, the chimney may be removed by unscrewing the nut inside the smokebox.
You will need to shorten the exhaust and I suggest you do this in two stages. First cut the exhaust just below the standard chimney so that it can be easily removed. Then bend the exhaust as shown in the drawing below so that there is straight pipe entering the chimney. Then with the chimney in place and the extension fitted, mark the exhaust at the bottom of the extension. Remove the chimney to allow you to unscrew the pipe and then mark the pipe 3mm above your first mark. Cut the pipe here and clean up the end with a file.
Now re-fit the exhaust and the chimney - then pish the SCGP9 chuffer into place. The top should be about 2mm down from the top of the chimney. Use black paint or chemical blackener to disguise it.