Hi Bertel,
There are probably people better qualified than me to comment but I will give you what information I have.
What year is your car? Chassis number?
My car (from South Africa is 1955 and is fitted with an older engine No. AM0459 which is a perfo engine dating, I think, from 1948. It would have been fitted with an 11D engine (shell big-ends and mains? and a different head). There may be other differences. The documentation that I have records that the engine was changed from No. 10521 006. This suggests that a different numbering system may have been adopted for 11D engines. Maybe others with 11D engines can comment.
Roger