Cutting and deburring the housing will take about  5 minutes.

Remove seal ring.   It is a little oily and particles from cutting will stick to it.

Cut the tube on the tappered transition.   

There are burrs and derbies after cutting to be removed.

Cut the 23 mm long lamp back up ring from the end piece.  The end of the tube has a small taper therefore reducing the diameter slightly.     The lamp will be inserted in the cut side of the back up ring. 

Deburr/sand the cut ends of both pieces after cutting.