Hi John, Gunter
The ZBV,s according to MG Saloon Cars by Clausager on page 185 some of the single colour cars did not have the dividing strip, the sunroofs were factory fitted on a few later cars, how this was done is not clear.
There were some specific variations carried out on the production cars at this time according to customer requests, Mike Elman-Brown had a MGA twin Cam built several months after production had finished.
Some of the ZA/ZB's had very special colours again laid out on page 185 of the above book, My car was Kashmir/maroon from new , chassis number 32690 so it is quite a late car, only about 200 cars seem to have been in this colour combo.
I suppose production was very low volumes during the 1950's and early 1960's
Trevor