Further to our chat earlier, your photo of the inside of your timing chest tells me that you are missing what C W Waller calls "the all-important flange" around the hole for the magneto shaft. Hopefully someone can provide a photo of this which should make all clear to you.
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.