The original Morgan column switch came from a Triumph Herald IIRC, but a standard one won't fit, you need to put an S bend into the shaft. This is a pretty fraught exercise, since (1) they are quite expensive and (2) there's a danger of kinking the tube.
I've done it twice now, I wrapped the stem in spiral banding to protect it and used the jaws of my bench vice to brace it whilst I put the bends in.
