Hello Piet, welcome to the forum.
I do not hold full details of the body codes but from what I have it would suggest the number might be Z21708 as Z28708 would appear to have been part of the 4 door production line.
Have you any other details about the car you can give us, like front window type, has it got factory fitted seat belt anchorage points, etc. An engine size, number might help although it could have been changed.
will be able to check for you, I'm sure they will help out very soon.
Hopefully all will be correct and you will be able to join in with all the advice and fun of the forum.