For this loco the chimney needs to be extended inside the smokebox to give better resonance. This can be turned on a lathe as a press fit extension, rolled from thin brass or tinplate, or made using  21/32" K&S tube which is the largest sold in metal centres.

 

Using the 21/32" tube, cut one piece 50mm long and two pieces 18mm long using a fine saw. Clean up the cuts with a fine file or abrasive paper. Then slit both 18mm tubes with the saw or with strong scissors. On one of the tubes remove a 5mm wide piece.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Now push the two tubes over one end of the 50mm tube as shown below. Trial fit this in the chimney and squeeze the three tubes to make a firm fit in the chimney. If it will not fit, remove a little more from the outer tube until it fits tightly inside the loco chimney.