Thank you! I will be getting that book.
Whatever its age it looks wonderful!
I hadn't realised that this transnational "Bustle Back" existed and rather like it. It brings together the best of the 4 seater and 2 seater.
According to Worrall & Turners book the bustle back was discontinued from chassis number 4023, in October 1958 when the sloping rear and off set fuel filler cap arrived. There are no photos but there is a reference in the list of production changes on page 65.
So your car has to have been built be prior to October 58.
The first car with the TR3 engine was 3421 in 1954, so it should be a Triumph TR3 motor.
Hope this helps, the book Original Morgan is available on eBay and Amazon.