Period correct would be the right one of the uppermost two pcitures. Anything with the blue strip and the newer typefont came in the 90s.
You need the simple old font pure black and white
The proper script would be
XX - XX 999
Wherby anything before the hyphen would be the city it was registered (one to 3 characters (a list is on the website you linked))
then 1 or two characters in the middle (after the hyphen, before the numbers). These are random (though some combinations were never issued (such as the obvious SS or NS or such). Also some combinations of city and characters were not issued (such as FU-CK..., although interestingly S-EX has been issued...)
Then lastly 1 to 4 digits (though 4 could not be period correct. 4 were issued only in larger citys and only beginning in the late 80s). Of course short and attractive combinations were popular (and you could try to get them depending on wheter or not you were friends with the major...)
So most likely would be something such as
B - AS 998
or
FFB - HG 38
for an E9
then there´s the issue of the seals / stamps
There would be a seal from the issuing city on both front and rear plate, placed under the hyphen
on the back plate there would be the (TÜV-Plakette), the stamp by the technical testing organisation that had to be renewed every two years (with rotating colours). Placed above the hyphen
Any questions, feel free to ask, I´m german and old enough to know...
